Index

Found 405 pages:

#	Page	Tags and summary
1	Glossary	Beginner, Glossary, Index, Landing
		Web technologies contain long lists of jargon and abbreviations that are used in documentation and coding. This glossary provides definitions of words and abbreviations you need to know to successfully understand and build for the web.
2	404	Glossary, HTTP Errors, Infrastructure, Navigation
		A 404 is a Standard Response Code meaning that the server cannot find the requested resource.
3	502	502, Glossary, HTTP Errors, Infrastructure, Navigation
		An HTTP error code meaning "Bad Gateway".
4	AJAX	AJAX, CodingScripting, Glossary, Infrastructure, l10n:priority
		AJAX (Asynchronous JavaScript And XML) is a programming practice of combining HTML, CSS, JavaScript, the DOM, and the XMLHttpRequest object to build more complex webpages.  What AJAX allows you to do is just update parts of a webpage instead of having to reload the entire page. AJAX also lets you work asynchronously, meaning your code continues to run while that part of your webpage is trying to reload (compared to synchronously which will block your code from running until that part of your webpage is done reloading).
5	API	CodingScripting, Glossary, Infrastructure
		An API (Application Programming Interface) is a set of features and rules that exist inside a software program enabling interaction between the software and other items, such as other software or hardware.
6	ARIA	Accessibility, Glossary
		ARIA (Accessible Rich Internet Applications) is a W3C specification for adding semantics and other metadata to HTML to cater to users of assistive technology.
7	ARPA	Glossary, Infrastructure
		Editorial review completed.
8	ASCII	Glossary, Infrastructure
		ASCII (American Standard Code for Information Interchange) is one of the most popular coding method used by computers for converting letters, numbers, punctuation and control codes into digital form. Since 2007, UTF-8 superseded it on the Web.
9	ATAG	ATAG, Accessibility, Authoring Tool Accessibility Guidelines, Glossary
		ATAG (Authoring Tool Accessibility Guidelines) is a W3C recommendation for building accessible-authoring tools that produce accessible contents.
10	Abstraction	Abstraction, Coding, CodingScripting, Glossary, Programming Language
		Abstraction in computer programming is a way to reduce complexity and allow efficient design and implementation in complex software systems. It hides the technical complexity of systems behind simpler APIs.
11	Accessibility	Accessibility, Glossary
		Web Accessibility (A11Y) refers to best practices for keeping a website usable despite physical and technical restrictions. Web accessibility is formally defined and discussed at the W3C through the Web Accessibility Initiative (WAI).
12	Adobe Flash	CodingScripting, Flash, Glossary, Infrastructure
		Technical review completed.
13	Algorithm	CodingScripting, Glossary
		An algorithm is a self-contained series of instructions that perform a function.
14	Apple Safari	Glossary, Navigation, WebMechanics
		Safari is a Web browser developed by Apple and bundled with both Mac OS X and iOS. It's based on the open source WebKit engine.
15	Application Context	CodingScripting, Glossary, glossary
		An application context is a top-level browsing context that has a manifest applied to it.
16	Argument	CodingScripting, Glossary, JavaScript
		An argument is a value (primitive or object) passed as input to a function.
17	Arpanet	Glossary, Infrastructure
		The ARPAnet (advanced research projects agency network) was an early computer network, constructed in 1969 as a robust medium to transmit sensitive military data and to connect leading research groups throughout the United States. ARPAnet first ran NCP (network control protocol) and subsequently the first version of the Internet protocol or TCP/IP suite, making ARPAnet a prominent part of the nascent Internet. ARPAnet was closed in early 1990.
18	Array	Array, CodingScripting, Glossary, JavaScript, programming
		An array is an ordered collection of data (either primitive or object depending upon the language). Arrays are used to store multiple values in a single variable. This is compared to a variable that can store only one value.
19	Asynchronous	Glossary, Web, WebMechanics
		Asynchronous refers to a communication environment where each party receives and processes messages when convenient or possible rather than immediately.
20	Attribute	CodingScripting, Glossary, HTML
		An attribute extends a tag, changing its behavior or providing metadata. An attribute always has the form name=value (the attribute's identifier followed by its associated value).
21	Bandwidth	Glossary, Infrastructure
		Technical review completed.
22	BiDi	Accessibility, Glossary
		BiDi (BiDirectional) refers to a document containing both right-to-left and left-to-right text. Even when both directionalities occur in the same paragraph, the text in each language must appear in its proper directionality.
23	Blink	Glossary, Infrastructure, Layout
		Blink is an open-source browser layout engine developed by Google as part of Chromium (and therefore part of Chrome as well). Specifically, Blink is a fork of the WebCore library in WebKit, which handles layout, rendering, and DOM.
24	Block	Disambiguation, Glossary
		The term block can have several meanings depending on the context. It may refer to:
25	Block (CSS)	CSS, CodingScripting, Design, Glossary, HTML
		A block on a webpage is an HTML element that appears on a new line, i.e. underneath the preceding element and above the following element (commonly known as a block-level element). For example, <p> is by default a block-level element, whereas <a> is an inline element — you can put several links next to one another in your HTML source and they will sit on the same line as one another in the rendered output.
26	Block (scripting)	CodingScripting, Glossary, JavaScript
		In JavaScript, a block is a collection of related statements enclosed in braces ("{}"). For example, you can put a block of statements after an if (condition) block, indicating that the interpreter should run the code inside the block if the condition is true, or skip the whole block if the condition is false.
27	Boolean	Boolean, CodingScripting, Glossary, JavaScript, Programming Languages, data types
		In computer science, a boolean is a logical data type that can have only the values true or false.
28	Boot2Gecko	Boot2Gecko, Firefox OS, Glossary, Infrastructure, Intro
		Boot2Gecko (B2G) is the engineering codename for Firefox OS and refers to builds that haven't yet received official Firefox OS branding. (Firefox OS was also often called Boot2Gecko before the project had an official name.)
29	Bounding Box	Bounding Box, CodingScripting, Design, Glossary, glossary
		The bounding box of an element is the smallest possible rectangle (aligned with the axes of that element's user coordinate system) that entirely encloses it and its descendants.
30	Browser	Glossary, Navigation
		A Web browser is a program that retrieves and displays pages from the Web, and lets users access further pages through hyperlinks.
31	Browsing context	CodingScripting, Glossary
		A browsing context is the environment in which a browser displays a Document (normally a tab nowadays, but possibly also a window or a frame within a page).
32	CDN	Glossary, Infrastructure
		A CDN (Content Delivery Network) is a group of servers spread out over many locations. These servers store duplicate copies of data so that servers can fulfill data requests based on which servers are closest to the respective end-users. CDNs make for fast service less affected by high traffic.
33	CIA	Glossary, Security
		CIA (Confidentiality, Integrity, Availability) (also called the CIA triad or AIC triad) is a model that guides an organization's policies for information security.
34	CMS	CMS, Composing, Content management system, Glossary
		A CMS (Content Management System) is software that allows users to publish, organize, change, or remove various kinds of content, not only text but also embedded images, video, audio, and interactive code.
35	CORS	Glossary, Infrastructure, Security
		CORS (Cross-Origin Resource Sharing) is a system, consisting of transmitting HTTP headers, that determines whether to block or fulfill requests for restricted resources on a web page from another domain outside the domain from which the resource originated.
36	CRLF	CR, CRLF, Glossary, Infrastructure, LF, carriage return, glossary, line feed
		CR and LF are control characters or bytecode that can be used to mark a line break in a text file.
37	CRUD	Glossary, Infrastructure
		CRUD (Create, Read, Update, Delete) is an acronym for ways one can operate on stored data. It is a mnemonic for the four basic functions of persistent storage.  CRUD typically refers to operations performed in a database or datastore, but it can also apply to higher level functions of an application such as soft deletes where data is not actually deleted but marked as deleted via a status.
38	CSP	Glossary, HTTP, Infrastructure
		A CSP (Content Security Policy) is used to detect and mitigate certain types of website related attacks like XSS and data injections.
39	CSRF	Glossary, Security
		CSRF (Cross-Site Request Forgery) is an attack that impersonates a trusted user and sends a website unwanted commands. This can be done, for example, by including malicious parameters in a URL behind a link that purports to go somewhere else.
40	CSS	CSS, CodingScripting, Glossary, Web, l10n:priority
		CSS (Cascading Style Sheets) is a declarative language that controls how webpages look in the browser.
41	CSS preprocessor	CSS
		A CSS preprocessor is a program that lets you generate CSS from the preprocessor's own unique syntax.
42	Cacheable	Glossary, WebMechanics
		A cacheable response is an HTTP response that can be cached, that is stored to be retrieved and used later, saving a new request to the server. Not all HTTP responses can be cached, there are the following constraints for an HTTP response to be cached:
43	CalDAV	CalDAV, Glossary, Infrastructure
		CalDAV (Calendaring extensions to WebDAV) is a protocol standardized by the IETF and used to remotely access calendar data from a server.
44	Call stack	Call Stack, CodingScripting, Glossary
		A call stack is a mechanism for an interpreter (like the JavaScript interpreter in a web browser) to keep track of its place in a script that calls multiple functions — what function is currently being run, what functions are called from within that function and should be called next, etc.
45	Callback function	Callback, Callback function, Glossary
		A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.
46	Canonical order	Canonical order, CodingScripting, Glossary
		In CSS, canonical order is used to refer to the order in which separate values need to be specified (or parsed) or are to be serialized as part of a CSS property value. It is defined by the formal syntax of the property and normally refers to the order in which longhand values should be specified as part of a single shorthand value.
47	Canvas	CodingScripting, Glossary, Graphics, HTML, JavaScript
		No summary!
48	Card sorting	Card sorting, Design, Glossary, glossary
		Card sorting is a simple technique used in Information architecture whereby people involved in the design of a website (or other type of product) are invited to write down the content / services / features they feel the product should contain, and then organize those features into categories or groupings. This can be used for example to work out what should go on each page of a website. The name comes from the fact that often card sorting is carried out by literally writing the items to sort onto cards, and then arranging the cards into piles.
49	CardDAV	CardDAV, Glossary, Infrastructure
		CardDAV (vCard Extension to WebDAV) is a protocol standardized by the IETF and used to remote-access or share contact information over a server.
50	Certificate authority	Cryptography, Glossary, Security
		A certificate authority (CA) is an organization that signs digital certificates and their associated public keys. This certifies that an organization that requested a digital certificate (e.g., Mozilla Corporation) is authorized to request a certificate for the subject named in the certificate (e.g., mozilla.org).
51	Certified	Apps, Firefox OS, Glossary, Security, Trustworthy
		Certified means that an application, content or data transmission has successfully undergone evaluation by professionals with expertise in the relevant field, thereby indicating completeness, security and trustworthiness.
52	Challenge-response authentication	Security
		In security protocols, a challenge is some data sent to the client by the server in order to generate a different response each time. Challenge-response protocols are one way to fight against replay attacks where an attacker listens to the previous messages and resends them at a later time to get the same credentials as the original message.
53	Character	CodingScripting, Glossary, strings
		A character is either a symbol (letters, numbers, punctuation) or non-printing "control" (e.g., carriage return or soft hyphen).  UTF-8 is the most common character set and includes the graphemes of the most popular human languages.
54	Character encoding	Composing, Glossary
		Character encoding provides an encoding system for specific characters in different languages, to allow them all to exist and be handled consistently in a computer system or programming environment.
55	Chrome	Browser, Chrome, Glossary, WebMechanics
		In a browser, the chrome is any visible aspect of a browser aside from the webpages themselves (e.g., toolbars, menu bar, tabs). This is not to be confused with the Google Chrome browser.
56	Cipher	Cryptography, Glossary, Privacy, Security
		In cryptography, a cipher is an algorithm that can encode cleartext to make it unreadable, and to decode it back.
57	Cipher suite	Cryptography, Glossary, Security
		A cipher suite is a combination of a key exchange algorithm, authentication method, bulk encryption cipher, and message authentication code.
58	Ciphertext	Cryptography, Glossary, Privacy, Security
		In cryptography, a ciphertext is a scrambled message that conveys information but is not legible unless decrypted with the right cipher and the right secret (usually a key), reproducing the original cleartext. A ciphertext's security, and therefore the secrecy of the contained information, depends on using a secure cipher and keeping the key secret.
59	Class	CodingScripting, Glossary
		In object-oriented programming, a class defines an object's characteristics. Class is a template definition of an object's properties and methods, the "blueprint" from which other more specific instances of the object are drawn.
60	Closure	CodingScripting, Glossary
		The binding which defines the scope of execution. In JavaScript, functions create a closure context.
61	Codec	Glossary, WebMechanics
		A codec  (a derivative from "coder-decoder") is a computer program that encodes or decodes a data stream.
62	Compile	CodingScripting, Glossary
		Compiling is the process of transforming a computer program in a given programming language into the same program written in another language (normally a binary language that the computer can execute).
63	Compile time	CodingScripting, Glossary, JavaScript
		The compile time is the time from when the program is first loaded until the program is parsed.
64	Computer Programming	CodingScripting, Computer Programming, Programming Language, programming
		Computer programming is a process of composing and organizing a collection of instructions. These tell a computer/software program what to do in a language which the computer understands. These instructions come in the form of many different languages such as C++, Java, JavaScript, HTML, Python, Ruby, and Rust.
65	Conditional	Beginner, CodingScripting, Glossary
		A condition is a set of rules that can interrupt normal code execution or change it, depending on whether the condition is completed or not.
66	Constant	CodingScripting, Constant, Glossary
		A constant is a value that the programmer cannot change, for example numbers (1, 2, 42). With variables, on the other hand, the programmer can assign a new value to a variable name already in use.
67	Constructor	CodingScripting, Glossary
		A constructor belongs to a particular class object that is instantiated. The constructor initializes this object and can provide access to its private information. The concept of a constructor can be applied to most object-oriented programming languages. Essentially, a constructor in JavaScript is usually declared at the instance of a class.
68	Control flow	CodingScripting, Glossary, JavaScript
		The control flow is the order in which the computer executes statements in a script.
69	Cookie	Glossary, WebMechanics
		A cookie is a small piece of information left by a website on a visitor's computer by a website, via a web browser.
70	Copyleft	Glossary, OpenPractices, Remixing, Sharing
		Copyleft is a term, usually referring to a license, used to indicate that such license requires that redistribution of said work is subject to the same license as the original. Examples of copyleft licenses are the GNU GPL (for software) and the Creative Commons SA (Share Alike) licenses (for works of art).
71	Crawler	Browser, Crawler, Glossary, Infrastructure
		A web crawler is a program, often called a bot or robot, which systematically browses the Web to collect data from webpages.  Typically search engines use crawlers to build indexes.
72	Cross-site scripting	Cross Site Scripting, DOM, Glossary, Security, XSS
		Technical review completed. Editorial review completed.
73	Cryptanalysis	Cryptography, Glossary, Privacy, Security
		Cryptanalysis is the branch of cryptography that studies how to break codes and cryptosystems. Cryptanalysis creates techniques to break ciphers, in particular by methods more efficient than a brute-force search. In addition to traditional methods like frequency analysis and index of coincidence, cryptanalysis includes more recent methods, like linear cryptanalysis or differential cryptanalysis, that can break more advanced ciphers.
74	Cryptographic hash function	Cryptography, Glossary, Security
		A cryptographic hash function is a cryptographic primitive transforming a message of arbitrary size into a message of fixed size, called a digest. Cryptographic hash functions are used for authentication, digital signatures, and message authentication codes.
75	Cryptography	Cryptography, Glossary, Privacy, Security
		Cryptography, or cryptology, is the science that studies how to encode and transmit messages securely. Cryptography designs and studies algorithms used to encode and decode messages in an insecure environment, and their applications.
76	DHTML	CodingScripting, DHTML, Glossary, HTML
		DHTML (Dynamic HTML) refers to the code behind interactive webpages that need no plugins like Flash or Java. DHTML aggregates the combined functionality of HTML, CSS, the DOM, and JavaScript.
77	DMZ	Glossary, Networking, Security
		A DMZ is a way to provide an insulated secure interface between what an internal network (corporate or private) and the outside untrusted world, usually: the internet.
78	DNS	DNS, Domain Name System, Glossary, Infrastructure
		DNS (Domain Name System) translates easy-to-recall domain names to the numerical IP addresses needed to find a particular computer service on the Internet or private network.
79	DOM	CodingScripting, DOM, Glossary
		The DOM (Document Object Model) is an API that represents and interacts with any HTML or XML document. The DOM is a document model loaded in the browser and representing the document as a node tree, where each node represents part of the document (e.g. an element, text string, or comment).
80	DTD	CodingScripting, Glossary
		<!DOCTYPE> informs the browser which version of HTML (or XML) you used to write the document. Doctype is a declaration, not a tag; you can also refer to it as "document type declaration", or "DTD" for short.
81	DTMF (Dual-Tone Multi-Frequency signaling)	DTMF, Glossary, WebRTC
		Dual-Tone Multi-Frequency (DTMF) signaling is a system by which audible tones are used to represent buttons being pressed on a keypad. Frequently referred to in the United States as "touch tone" (after the Touch-Tone trademark used when the transition from pulse dialing to DTMF began), DTMF makes it possible to signal the digits 0-9 as well as the letters "A" through "D" and the symbols "#" and "*". Few telephone keypads include the letters, which are typically used for control signaling by the telephone network.
82	Data structure	CodingScripting, Data structure, Glossary
		Data structure is a particular way of organizing data so that it can be used efficiently.
83	Decryption	Cryptography, Glossary, Privacy, Security
		In cryptography, decryption is the conversion of ciphertext into cleartext.
84	Denial of Service	Attack, Denial of Service, Glossary, Intro, Security
		DOS (Denial of service) is an attack on computers or networks that restricts or prevents legitimate use. In a DOS attack, an attacker uses a flood of packets to slow down or crash the target system or an entire network.
85	Descriptor (CSS)	CodingScripting, Glossary
		No summary!
86	Developer Tools	CodingScripting, Developer Tools, Glossary
		Developer tools (or "development tools" or short "DevTools") are programs that allow a developer to create, test and debug software.
87	Digest	Cryptography, Glossary, Privacy, Security
		A digest is a small value generated by a hash function from a whole message. Ideally, a digest is quick to calculate, irreversible, and unpredictable, and therefore indicates whether someone has tampered with a given message.
88	Digital certificate	Cryptography, Glossary, Security
		A digital certificate is a data file that binds a publicly known cryptographic key to an organization.
89	Distributed Denial of Service	Attack, DDoS, Denial of Service, Glossary, Intro, Security
		A Distributed Denial-of-Dervice (DDoS) is an attack in which many compromised systems are made to attack a single target, in order to swamp server resources and block legitimate users.
90	DoS attack	Glossary, Security
		DoS (Denial of Service) is a network attack that prevents legitimate use of server resources by flooding the server with requests.
91	Doctype	Browser, CodingScripting, DOCTYPE, Glossary, HTML, Intro
		In HTML, the doctype is the required "<!DOCTYPE html>" preamble found at the top of all documents. Its sole purpose is to prevent a browser from switching into so-called “quirks mode” when rendering a document; that is, the "<!DOCTYPE html>" doctype ensures that the browser makes a best-effort attempt at following the relevant specifications, rather than using a different rendering mode that is incompatible with some specifications.
92	Document directive	CSP, HTTP, Security
		CSP document directives are used in a Content-Security-Policy header and govern the properties of a document or worker environment to which a policy applies.
93	Domain	Browser, Domain, Infrastructure, Networking
		A domain is the part of a computer network in which one entity controls the data processing resources, for example a website.
94	Domain name	Domain Name, Glossary, Protocol, WebMechanics
		A domain name is a website's address on the Internet. Domain names are used in URLs to identify to which server belong a specific webpage. The domain name consists of a hierarchial sequence of names (labels) separated by periods (dots) and ending with an extension.
95	Dominator	CodingScripting, Glossary, glossary
		In graph theory, node A dominates node B if every path from the root node to B passes through A.
96	Dynamic programming language	CodingScripting, Glossary
		A dynamic programming language is a programming language in which operations otherwise done at compile-time can be done at run-time. For example, in JavaScript it is possible to change the type of a variable or add new properties or methods to an object while the program is running.
97	Dynamic typing	CodingScripting, Glossary, ProgrammingLanguage
		Dynamically-typed languages are those (like JavaScript) where the interpreter assigns variables a type at runtime based on the variable's value at the time.
98	ECMA	Glossary, Stub, WebMechanics
		Ecma International (formally European Computer Manufacturers Association) is a non-profit organization that develops standards in computer hardware, communications, and programming languages.
99	ECMAScript	Glossary, WebMechanics
		ECMAScript is the scripting language on which JavaScript is based. Ecma International is in charge of standardizing ECMAScript.
100	Element	CodingScripting, Glossary, HTML
		An element is a part of a webpage. In XML and HTML, an element may contain a data item or a chunk of text or an image, or perhaps nothing. A typical element includes an opening tag with some attributes, enclosed text content, and a closing tag:
101	Empty element	CodingScripting, Glossary, Intermediate
		An empty element is an element from HTML, SVG, or MathML that cannot have any child nodes (i.e., nested elements or text nodes).
102	Encapsulation	CodingScripting, Glossary
		Encapsulation is the packing of data and functions into one component (for example, a class) and then controlling access to that component to make a "blackbox" out of the object. Because of this, a user of that class only needs to know its interface (that is, the data and functions exposed outside the class), not the hidden implementation.
103	Encryption	Cryptography, Glossary, Privacy, Security
		In cryptography, encryption is the conversion of cleartext into a coded text or ciphertext. A ciphertext is intended to be unreadable by unauthorized readers.
104	Endianness	Coding, CodingScripting, Glossary
		"Endian" and "endianness" (or "byte-order") describe how computers organize the bytes that make up numbers.
105	Engine	CodingScripting, Glossary, NeedsContent
		Technical review completed.
106	Entity	CodingScripting, Composing, Glossary, HTML
		An HTML entity is a piece of text ("string") that begins with the ampersand (&) character and ends with the semicolon (;) character.  Often, users employ entities to display characters that are normally interpreted as HTML code, invisible characters such as the non-breaking space, or characters that are difficult to type with a standard keyboard.
107	Entity header	Glossary, WebMechanics
		An entity header is an HTTP header describing the content of the body of the message. Entity headers are used in both, HTTP requests and responses. Headers like Content-Length, Content-Language, Content-Encoding are entity headers.
108	Event	CodingScripting, Glossary
		Events are assets generated by DOM elements, which can be manipulated by a Javascript code.
109	Exception	Beginner, CodingScripting, Glossary
		An exception is a condition that interrupts normal code execution. In JavaScript syntax errors are a very common source of exceptions.
110	Expando	CodingScripting, JavaScript, Reference, expando
		Expando properties are properties added to DOM nodes with JavaScript, where those properties are not part of the object's DOM specification:
111	FTP	CodingScripting, FTP, Glossary, Protocol
		FTP (File Transfer Protocol) was the standard protocol for many years for transferring files from one host to another over the Internet. Increasingly, though, teams and hosting accounts don't allow FTP and instead rely on a version control system like Git. You will still find it used on older hosting accounts, but it is safe to say that FTP is no longer considered best practice.
112	FTU	FTU, Firefox OS, First time use, Gaia, Glossary, Infrastructure, Intro
		FTU (First Time Use) is the app that loads when you run a newly-installed version of Gecko on a Firefox OS device.
113	Falsy	CodingScripting, Glossary, JavaScript
		A falsy value is a value that translates to false when evaluated in a Boolean context.
114	Fetch directive	CSP, HTTP, Security
		CSP fetch directives are used in a Content-Security-Policy header and control locations from which certain resource types may be loaded. For instance, script-src allows developers to allow trusted sources of script to execute on a page, while font-src controls the sources of web fonts.
115	Firefox OS	Boot2Gecko, Firefox OS, Glossary, Infrastructure, Intro
		Firefox OS is Mozilla's mobile operating system, based on Linux and Firefox's powerful Gecko rendering engine. Firefox OS consists mainly of Gaia, Gecko, and Gonk.
116	First-class Function	CodingScripting, Glossary
		A programming language is said to have First-class functions when functions in that language are treated like any other variable. For example, in such a language, a function can be passed as an argument to other functions, can be returned by another function and can be assigned as a value to a variable.
117	Forbidden header name	Fetch, Glossary, HTTP, Headers, forbidden
		A forbidden header name is an HTTP header name that cannot be modified programmatically; specifically, an HTTP request header name.
118	Forbidden response header name	Glossary, HTTP, Response, forbidden
		A forbidden response header name is an HTTP header name (either `Set-Cookie` or `Set-Cookie2`) that cannot be modified programmatically.
119	Function	CodingScripting, Glossary, IIFE, Immediately Invoked Function Expressions (IIFE), JavaScript
		A function is a code snippet that can be called by other code or by itself, or a variable that refers to the function. When a function is called, arguments are passed to the function as input, and the function can optionally return an output. A function in JavaScript is also an object.
120	GIF	Composing, Glossary, glossary
		Technical review completed.
121	GIJ	Automation, CodingScripting, Gaia, Integration, tests
		Gaia integration Testing. Marionette- and JavaScript- based. See GIJ.
122	GPL	GPL, Glossary, License, OpenPractices, Remixing, Sharing
		The (GNU) GPL (General Public License) is a copyleft free software license published by the Free Software Foundation. Users of a GPL-licensed program are granted the freedom to use it, read the source code, modify it and redistribute the changes they made, provided they redistribute the program (modified or unmodified) under the same license.
123	GPU	Glossary, Infrastructure
		The GPU (Graphics Processing Unit) is a computer component similar to the CPU (Central Processing Unit). It specializes in the drawing of graphics (both 2D and 3D) on your monitor.
124	GZip compression	Glossary, compression, gzip
		gzip is a compression algorithm that allows files to be made smaller in size, allowing for faster network transfers. It is commonly supported by web servers and modern browsers, meaning that servers can automatically compress files with gzip before sending them, and browsers can uncompress files upon receiving them.
125	Gaia	Boot2Gecko, Firefox OS, Gaia, Glossary, Infrastructure, Intro
		The user interface and default application suite of the Firefox OS platform.
126	Garbage collection	CodingScripting, Glossary, glossary
		Garbage collection is a term used in computer programming to describe the process of finding and deleting objects which are no longer being referenced by other objects.
127	Gecko	Firefox OS, Gecko, Glossary, Infrastructure, Intro, Mozilla
		Gecko is the layout engine developed by the Mozilla Project and used in many apps/devices, including Firefox and Firefox OS.
128	General header	Glossary, WebMechanics
		A general header is an HTTP header that can be used for both, request and response messages, but don't apply to the content itself. Depending on the context they are used in, general headers are either response or request headers. However, they are not entity headers.
129	Git	Collaborating, Glossary
		Git is a free, open-source, distributed Source Code Management (SCM) system. It facilitates handling code bases with distributed development teams. What sets it apart from previous SCM systems is the ability to do common operations (branching, committing, etc.) on your local development machine, without having to change the master repository or even having write access to it.
130	Global attribute	Attribute, CodingScripting, Glossary, HTML
		Global attributes are attributes that can be used on all elements (though sometimes without effect on some elements).
131	Global object	CodingScripting, Glossary, NeedsContent
		A global object is an object that always exists in the global scope.
132	Global scope	CodingScripting, Glossary, NeedsContent
		In a programming environment, the global scope is the scope that contains, and is visible in, all other scopes.
133	Global variable	CodingScripting, Glossary
		A global variable is a  variable that is declared in the global scope in other words, a variable that is visible from all other scopes.
134	Gonk	Boot2Gecko, Firefox OS, Glossary, Gonk, Infrastructure, Intro
		Gonk is the lower-level operating system of Firefox OS and consists of a Linux kernel (based on the Android Open Source Project (AOSP)) and userspace hardware abstraction layer (HAL).
135	Google Chrome	Browser, Chrome canary, Chrome stable, Chromium, Glossary, WebMechanics, google chrome
		Google Chrome is a free Web browser developed by Google. It's based on the Chromium open source project. Some key differences are described on the Chromium wiki. For a layout engine, both browsers use a fork of WebKit called Blink. Note that the iOS version of Chrome uses that platform's rendering engine, not Blink.
136	Graceful degradation	Design, Glossary, graceful degradation
		Graceful degradation is a design philosophy that centers around trying to build a modern web site/application that will work in the newest browsers, but fall back to an experience that while not as good still delivers essential content and functionality in older browsers.
137	Grid	CSS, CSS Grids
		Technical review completed. Editorial review completed.
138	Grid Areas	CSS Grids
		A grid area is one or more grid cells that make up a rectangular area on the grid. Grid areas are created when you place an item using line-based placement or when defining areas using named grid areas.
139	Grid Axis	CSS, CSS Grids
		CSS Grid Layout is a two-dimensional layout method enabling the laying out of content in rows and columns. Therefore in any grid we have two axes. The block or column axis, and the inline or row axis.
140	Grid Cell	CSS Grids
		In a CSS Grid Layout, a grid cell is the smallest unit you can have on your CSS grid. It is the space between four intersecting grid lines and conceptually much like a table cell.
141	Grid Column	CSS, CodingScripting
		A grid column is a vertical track in a CSS Grid Layout, and is the space between two vertical grid lines. It is defined by the grid-template-columns property or in the shorthand grid or grid-template properties.
142	Grid Lines	CSS Grids
		Grid lines are created when you define tracks in the explicit grid using CSS Grid Layout. In the following example there is a grid with three column tracks and two row tracks. This gives us 4 column lines and 3 row lines.
143	Grid Row	CSS Grids
		A grid row is a horizontal track in a CSS Grid Layout, that is the space between two horizontal grid lines. It is defined by the grid-template-rows property or in the shorthand grid or grid-template properties.
144	Grid Tracks	CSS Grids
		A grid track is the space between two grid lines. They are defined in the explicit grid by using the grid-template-columns and grid-template-rows properties or the shorthand grid or grid-template properties. Tracks are also created in the implicit grid by positioning a grid Item outside of the tracks created in the explicit grid.
145	Guard	API, CodingScripting, Glossary, guard
		Guard is a feature of Headers objects (as defined in the Fetch spec, which affects whether methods such as set() and append() can change the header's contents. For example, immutable guard means that headers can't be changed. For more information, read Fetch basic concepts: guard.
146	Gutters	CSS Grids
		Gutters or alleys are spacing between content tracks. These can be created in CSS Grid Layout using the grid-column-gap, grid-row-gap, or grid-gap properties.
147	HMAC	Cryptography, Glossary, Hash, Security
		HMAC is a protocol used for cryptographically authenticating messages.
148	HPKP	Glossary, Security, glossary
		HTTP Public Key Pinning (HPKP) is a security feature that tells a web client to associate a specific cryptographic public key with a certain web server to decrease the risk of MITM attacks with forged certificates.
149	HSTS	HTTP, Security
		HTTP Strict Transport Security lets a web site inform the browser that it should never load the site using HTTP and should automatically convert all attempts to access the site using HTTP to HTTPS requests instead. It consists in one HTTP header, Strict-Transport-Security, sent back by the server with the resource.
150	HTML	CodingScripting, Glossary, HTML, l10n:priority
		HTML (HyperText Markup Language) is a descriptive language that specifies webpage structure.
151	HTML5	CodingScripting, Glossary, HTML, HTML5
		The latest stable release of HTML, HTML5 takes HTML from a simple markup for structuring a document to a full app development platform. Among other features, HTML5 includes new elements and JavaScript APIs to enhance storage, multimedia, and hardware access.
152	HTTP	Beginner, Glossary, HTTP, Infrastructure, l10n:priority
		HTTP (HyperText Transfer Protocol) is the basic protocol that enables file transfer on the Web. HTTP is textual (all communication is done in plain text) and stateless (no communication is aware of previous communications).
153	HTTPS	Glossary, HTTPS, Infrastructure, Security, glossary
		HTTPS (HTTP Secure) is an encrypted version of the HTTP protocol. It usually uses SSL or TLS to encrypt all communication between a client and a server. This secure connection allows clients to safely exchange sensitive data with a server, for example for banking activities or online shopping.
154	Hash	CodingScripting, Cryptography, Glossary, Hash
		The hash function takes a variable length message input and produces a fixed-length hash output. It is commonly in the form of a 128-bit "fingerprint" or "message digest". Hashes are very useful for cryptography — they insure the integrity of transmitted data. This provides the basis for HMAC's, which provide message authentication.
155	Head	CodingScripting, Glossary, HTML, glossary, head, metadata
		The Head is the part of an HTML document that contains metadata about that document, such as author, description, and links to CSS or JavaScript files that should be applied to the HTML.
156	Header	Glossary, WebMechanics
		An HTTP header is a field of an HTTP request or response that passes additional information, altering or precising the semantics of the message or of the body. Headers are case-insensitive, begins at the start of a line and are immediately followed by a ':' and a value depending of the header itself. The value finish at the next CR or at the end of the message.
157	High-level programming language	CodingScripting, Glossary, glossary
		A high-level programming language has a significant abstraction from the details of computer operation. It is designed to be easily understood by humans and for this reason they must be translated by another software. Unlike low-level programming languages, it may use natural language elements, or may automate (or even entirely hide) significant areas of computing systems, making the process of developing simpler and more understandable relative to a lower-level language. The amount of abstraction provided defines how "high-level" a programming language is.
158	Hoisting	CodingScripting, Glossary, JavaScript
		Hoisting is a term you will not find used in any normative specification prose prior to ECMAScript® 2015 Language Specification. Hoisting was thought up as a general way of thinking about how execution context (specifically the creation and execution phases) work in JavaScript. But, hoisting can lead to misunderstandings. For example, hoisting teaches that variable and function declarations are physically moved to the top of your coding, but this is not what happens at all. What does happen is that variable and function declarations are put into memory during the compile phase, but stays exactly where you typed it in your coding.
159	Host	Glossary, Intermediate, Web, WebMechanics
		A host is a device connected to the Internet (or a local network). Some hosts called servers offer additional services like serving webpages or storing files and emails.
160	Hotlink	Glossary, WebMechanics, glossary
		A hotlink (also known as an inline link) is an object (typically an image) directly linked to from another site. For example, an image hosted on site1.com is shown directly on site2.com.
161	Hyperlink	CodingScripting, Glossary, HTML, Navigation
		Hyperlinks connect webpages or data items to one another. In HTML, <a> elements define hyperlinks from a spot on a webpage (like a text string or image) to another spot on some other webpage (or even on the same page).
162	Hypertext	Glossary, Web, WebMechanics, glossary
		Hypertext is text that contains links to other texts, as opposed to a single linear flow like in a novel.
163	I18N	Beginner, Credibility, Glossary, Internationalization, OpenPractices, i18n
		i18n (from "internationalization", a 20-letter word) is the best practice that enables products or services to be readily adapted to any target culture.
164	IANA	Glossary, Infrastructure
		IANA (Internet Assigned Numbers Authority) is a subsidiary of ICANN charged with recording and/or assigning domain names, IP addresses, and other names and numbers used by Internet protocols.
165	ICANN	Glossary, Infrastructure
		ICANN (Internet Corporation of Assigned Names and Numbers) is an international nonprofit that maintains the domain name system and the record of IP addresses.
166	ICE	CodingScripting, Glossary, Networking, Protocols, WebRTC
		ICE (Interactive Connectivity Establishment) is a framework used by WebRTC (among other technologies) for connecting two peers to each other, regardless of network topology (usually for audio and/or video chat). This protocol lets two peers find and establish a connection with one another even though they may both be using Network Address Translator (NAT) to share a global IP address with other devices on their respective local networks.
167	IDE	CodingScripting, Glossary
		An Integrated Development Environment (IDE) or Interactive Development environment is a software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of a source code editor, build automation tools and a debugger.
168	IDL	CodingScripting, Glossary, IDL, Interface description language
		An IDL (Interface Description Language) is a generic language used to specified objects' interfaces apart from any specific programming language.
169	IETF	Glossary, IETF, Infrastructure, Internet, glossary
		The Internet Engineering Task Force (IETF) is a worldwide organization that drafts specifications governing the mechanisms behind the Internet, especially the TCP/IP or Internet Protocol Suite.
170	IIFE	CodingScripting, Glossary, JavaScript
		Technical review completed. Editorial review completed.
171	IMAP	Beginner, Glossary, Infrastructure, MailNews
		IMAP (Internet Message Access Protocol) is a protocol used to retrieve and store emails. More recent than POP3, IMAP allows folders and rules on the server.
172	IP Address	Beginner, Glossary, Infrastructure, Web
		An IP address is a number assigned to every device connected to a network that uses the Internet protocol.
173	IPv4	Glossary, IPv4, Infrastructure, Internet Protocol, Protocol
		IPv4 is the fourth version of the communication protocol underlying the Internet and the first version to be widely deployed.
174	IPv6	Glossary, IPv6, Infrastructure, Intermediate, Web, WebMechanics
		IPv6 is the current version of the communication protocol underlying the Internet. Slowly IPv6 is replacing IPv4, among other reasons because IPv6 allows for many different IP addresses.
175	IRC	Glossary, Infrastructure, Internet Relay Chat, Open Protocol, irc
		IRC (Internet Relay Chat) is a worldwide chat system requiring an Internet connection and an IRC client, which sends and receives messages via the IRC server.
176	ISO	Glossary, ISO, Infrastructure, Web Standards, web specifications
		Technical review completed. Editorial review completed.
177	ISP	Glossary, ISP, Internet Service Provider, Web, WebMechanics
		An ISP (Internet Service Provider) sells Internet access, and sometimes email, web hosting, and voice over IP, either by a dial-up connection over a phone line (formerly more common), or through a broadband connection such as a cable modem or DSL service.
178	Idempotent	Glossary, WebMechanics
		An HTTP method is idempotent if an identical request can be made once or several times in a row with the same effect while leaving the server in the same state. In other words, an idempotent method should not have any side-effects (except for keeping statistics). Implemented correctly, the GET, HEAD, PUT, and DELETE method are idempotent, but not the POST method. All safe methods are also idempotent.
179	Identifier	Beginner, Glossary, Sharing
		A sequence of characters in the code that identifies a variable, function, or property.
180	Immutable	CodingScripting, Glossary
		An immutable object is one whose content cannot be changed. An object can be immutable for various reasons, for example:
181	Index	Glossary, Index, MDN Meta, Navigation
		Found 405 pages:
182	IndexedDB	API, CodingScripting, Database, Glossary, Sql
		IndexedDB is a Web API for storing large data structures within browsers and indexing them for high-performance searching. Like an SQL-based RDBMS, IndexedDB is a transactional database system. However, it uses JavaScript objects rather than fixed columns tables to store data.
183	Information architecture	Design, Glossary, glossary, information architecture
		Information architecture, as applied to web design and development, is the practice of organizing the information / content / functionality of a web site so that it presents the best user experience it can, with information and services being easily usable and findable.
184	Inheritance	CodingScripting, Glossary, Inheritance, Programming Language
		Inheritance is a major feature of object-oriented programming.  Data abstraction can be carried up several levels, that is, classes can have superclasses and subclasses.
185	Instance	Beginner, CodingScripting, Glossary, JavaScript, NeedsContent
		An object created by a constructor is an instance of that constructor.
186	Internet	Beginner, Glossary, Guide, Intro, NeedsContent, Tutorial, Web, WebMechanics
		The Internet is a worldwide network of networks that uses the Internet protocol suite (also named TCP/IP from its two most important protocols).
187	JPEG	Beginner, Composing, Glossary, JPEG
		JPEG (Joint Photographic Experts Group) is a commonly used method of lossy compression for digital images.
188	JSON	CodingScripting, Glossary, Intro, JSON, l10n:priority
		The JavaScript Object Notation (JSON) is a data-interchange format.  Although not a strict subset, JSON closely resembles a subset of JavaScript syntax. Though many programming languages support JSON, JSON is especially useful for JavaScript-based apps, including websites and browser extensions.
189	Jank	Beginner, CodingScripting, Glossary, Performance
		Jank refers to sluggishness in a user interface, usually caused by executing long tasks on the main thread, blocking rendering, or expending too much processor power on background processes.
190	Java	CodingScripting, Glossary, Java, Programming Language
		Java is an object-oriented, class-based, portable  computer programming language designed for minimal implementation dependencies.
191	JavaScript	CodingScripting, Glossary, JavaScript, l10n:priority
		JavaScript (JS) is a programming language mostly used client-side to dynamically script webpages, but often also server-side, using packages such as Node.js.
192	Key	Cryptography, Glossary, Security
		A key is a piece of information used by a cipher for encryption and/or decryption.
193	Keyword	Glossary, Keyword, Search, keyword search
		A keyword is a word or phrase that describes content.  Online keywords are used as queries for search engines or as words identifying content on websites.
194	LGPL	Glossary, License, OpenPractices, Remixing, Sharing
		LGPL (GNU Lesser General Public License) is a free software license published by the Free Software Foundation. The LGPL provides a more permissive alternative for the strictly copyleft GPL. While any derivative work using a GPL-licensed program must be released under the same terms (free to use, share, study, and modify), the LGPL only requires the LGPL-licensed component of the derivative program to continue using the LGPL, not the whole program. LGPL is usually used to license shared components such as libraries (.dll, .so, .jar, etc.).
195	Ligature	CSS, Design, Glossary
		A ligature is a joining of two characters into one shape. For example, in French "œ" is a ligature of "oe".
196	Local scope	CodingScripting, Glossary, NeedsContent
		Local scope is a characteristic of variables that makes them local (i.e., the variable name is only bound to its value within a scope which is not the global scope).
197	Local variable	CodingScripting, Glossary, NeedsContent
		A variable whose name is bound to its value only within a local scope.
198	Locale	Composing, Glossary, Locale
		Locale is a set of language- or country-based preferences for a user interface.
199	Localization	Collaborating, Glossary, Intro, Localization, WebMechanics
		Localization (l10n) is the process of adapting a software user interface to a specific culture.
200	MIME type	Glossary, WebMechanics
		A MIME type (now properly called "media type", but also sometimes "content type") is a string sent along with a file indicating the file type (for example, a sound file might be labeled audio/ogg, or an image file image/png). It serves the same purpose as filename extensions traditionally do on Windows.
201	MathML	CodingScripting, Glossary, MathML, Mathematical Markup Language, XML
		MathML (an XML application) is an open standard for representing mathematical expressions in webpages.  In 1998 the W3C first recommended MathML for representing mathematical expressions in the browser. MathML has other applications also including scientific content and voice synthesis.
202	Metadata	CodingScripting, Glossary, HTML, glossary, metadata
		Metadata is — in its very simplest definition — data that describes data. For example, an HTML document is data, but HTML can also contain metadata in its <head> element that describes the document — for example who wrote it, and its summary.
203	Method	CodingScripting, Glossary, JavaScript
		A method is a function which is a property of an object. There are two kind of methods: Instance Methods which are built-in tasks performed by an object instance, or Static Methods which are tasks that can be performed without the need of an object instance.
204	Microsoft Edge	Browser, Glossary, Infrastructure
		Microsoft Edge is a free-of-cost graphical Web browser bundled with Microsoft Windows and developed by Microsoft since 2014. Initially known as Spartan, Edge replaced the longstanding Microsoft browser Internet Explorer.
205	Microsoft Internet Explorer	Browser, Glossary, Internet Explorer, Microsoft, Microsoft Internet Explorer, Navigation, Web Browser, Windows, Windows Operating System
		Internet Explorer (or IE) is a free graphical browser maintained by Microsoft for legacy enterprise uses. Microsoft Edge is currently the default Windows browser.
206	Middleware	CodingScripting, Glossary, glossary
		Middleware is a (loosly defined) term for any software or service that enables the parts of a system to communicate and manage data. It is the software that handles communication between components and input/output, so developers can focus on the specific purpose of their application.
207	MitM	Glossary, Security, glossary
		A Man-in-the-middle attack (MitM) intercepts a communication between two systems. For example, a Wi-Fi router can be compromised.
208	Mixin	CodingScripting, Glossary, Method, Mixin, Property
		A mixin is a class or interface in which some or all of its methods and/or properties are unimplemented, requiring that another class or interface provide the missing implementations.
209	Mobile First	Design, Glossary, Layout, Layout mobile
		Mobile first, a form of progressive enhancement, is a web-development and web-design approach that focuses on prioritizing design and development for mobile screen sizes over design and development for desktop screen sizes. The rationale behind the mobile-first approach is to provide users with good user experiences at all screen sizes—by starting with creating a user experience that works well on small screens, and then building on top of that to further enrich the user experience as the screen size increases. The mobile-first approach contrasts with the older approach of designing for desktop screen sizes first, and then only later adding some support for small screen sizes.
210	Modem	Infrastructure, Navigation
		A modem ("modulator-demodulator") is a device that converts digital information to analog signals and vice-versa, for sending data through networks.
211	Modern web apps	Composing, Glossary, Modern web apps, glossary
		See Progressive web apps
212	Modularity	CodingScripting, Glossary, glossary
		The term Modularity refers to the degree to which a system's components may be separated and recombined, it is also division of a software package into logical units. The advantage of a modular system is that one can reason the parts independently
213	Mozilla Firefox	Browser, Firefox, Glossary, Infrastructure, Mozilla, Mozilla Firefox
		Mozilla Firefox is a free open-source browser whose development is overseen by the Mozilla Corporation. Firefox runs on Windows, OS X, Linux, and Android.
214	Mutable	CodingScripting, Glossary, NeedsContent
		Mutable is a type of variable that can be changed. In JavaScript, only objects and arrays are mutable, not primitive values.
215	NAT	Beginner, Glossary, Infrastructure, WebMechanics, WebRTC
		NAT (Network Address Translation) is a technique for letting multiple computers share an IP address. NAT assigns unique addresses to each computer on the local network and adjusts incoming/outgoing network traffic to send data to the right place.
216	NNTP	Glossary, Infrastructure
		NNTP (Network News Transfer Protocol) is a protocol used to transfer Usenet messages from client to server or between servers.
217	NaN	CodingScripting, Computing, Glossary, NaN
		NaN (Not a Number) is a numeric data type that means an undefined value or value that cannot be represented, especially results of floating-point calculations.
218	Namespace	CodingScripting, Glossary, Operating System
		Namespace is a context for identifiers, a logical grouping of names used in a program. Within the same context and same scope,  an identifier must uniquely identify an entity.
219	Native	CodingScripting, Glossary, glossary
		A native application has been compiled to run on the hardware/software environment that comprises the targeted architecture.
220	Navigation directive	CSP, HTTP, Security
		CSP navigation directives are used in a Content-Security-Policy header and govern to which location a user can navigate to or submit a form to, for example.
221	Netscape Navigator	Browser, Glossary, Navigation, Netscape, Netscape Navigator
		Netscape Navigator or Netscape was a leading browser in the 1990s.  Netscape was based on Mosaic and the Netscape team was led by Marc Andreessen, a programmer who also wrote code for Mosaic.
222	Node	Disambiguation, Glossary
		The term node can have several meanings depending on the context. It may refer to:
223	Node (DOM)	CodingScripting, Glossary
		In the context of the DOM, a node is a single point in the node tree. Various things that are nodes are the document itself, elements, text, and comments.
224	Node (networking)	Glossary, Infrastructure, glossary
		In networking, a node is a connection point in the network. In physical networks, a node is usually a device, like a computer or a router.
225	Node.js	Glossary, Infrastructure, JavaScript, node.js
		Node.js is a cross-platform JavaScript runtime environment that allows developers to build server-side and network applications with JavaScript.
226	Normative	Glossary, Infrastructure, Specification, Standardization, glossary
		Normative is a word commonly used in software specifications to denote sections that are standardized and must be followed as a rule. Specifications might also contain sections that are marked as non-normative or informative, which means those are provided there for the purpose of helping the reader understand the specifications better or to showcase an example or best practice, which need not be followed as a rule.
227	Null	CodingScripting, Glossary
		In computer science, a null value represents a reference that points, generally intentionally, to a nonexistent or invalid object or address. The meaning of a null reference varies among language implementations.
228	Number	CodingScripting, Glossary, JavaScript
		In JavaScript, Number is a numeric data type in the double-precision 64-bit floating point format (IEEE 754). In other programming languages different numeric types can exist, for examples: Integers, Floats, Doubles, or Bignums.
229	OOP	Beginner, CodingScripting, Glossary
		OOP (Object-Oriented Programming) is an approach in programming in which data is encapsulated within objects and the object itself is operated on, rather than its component parts.
230	OTA	Glossary, Infrastructure, Intro, OTA, Over the air, glossary, updates
		Over The Air (OTA) refers to automatic updating of software on connected devices from a central server. All device owners receiving a given set of updates are on the same "channel", and each device often can access several channels (e.g. for production or engineering builds).
231	OWASP	Glossary, Security
		OWASP (Open Web Application Security Project) is a non-profit organization and worldwide network that works for security in Free Software, especially on the Web.
232	Object	CodingScripting, Glossary, Intro, Object
		Object refers to a data structure containing data and instructions for working with the data. Objects sometimes refer to real-world things, for example a car or map object in a racing game. JavaScript, Java, C++, Python, and Ruby are examples of object-oriented programming languages.
233	Object reference	CodingScripting, Glossary
		A link to an object. Object references can be used exactly like the linked objects.
234	OpenGL	CodingScripting, Glossary, OpenGL
		Editorial review completed.
235	OpenSSL	Glossary, Security
		OpenSSL is an open-source implementation of SSL and TLS.
236	Opera Browser	Browser, Glossary, Navigation, Opera, Opera Browser
		Opera is the fifth most used web browser, publicly released in 1996 and initially running on Windows only. Opera uses Blink as its layout engine since 2013 (before that, Presto). Opera also exists in mobile and tablet versions.
237	Operand	CodingScripting, Glossary
		An operand is the part of an instruction representing the data manipulated by the operator. For example, when you add two numbers, the numbers are the operand and "+" is the operator.
238	Operator	CodingScripting, Glossary
		Editorial review completed.
239	Origin	Glossary, WebMechanics, origin
		Web content's origin is defined by the scheme (protocol), host (domain), and port of the URL used to access it. Two objects have the same origin only when the scheme, host, and port all match.
240	P2P	Glossary, Infrastructure, Networking, P2P
		P2P (Peer-to-peer) is a computer networking architecture in which all participating nodes (peers) have equal privileges and share the workload. P2P differs from a client-server network architecture, where multiple client nodes connect to centralized servers for services.
241	PAC	CodingScripting, Glossary, glossary
		A Proxy Auto-Configuration file (PAC file) is a file which contains a function, FindProxyForURL(), which is used by the browser to determine whether requests (including HTTP, HTTPS, and FTP) should go directly to the destination or if they need to be forwarded through a web proxy server.
242	PDF	Composing, Glossary, PDF, Portable Document Format
		PDF (Portable Document Format) is a file format used to share documentation without depending on any particular software implementation, hardware platform, or operating system. PDF provides a digital image of a printed document, and keeps the same appearance when printed.
243	PHP	CodingScripting, Glossary, Infrastructure, PHP
		Editorial review completed.
244	PNG	Beginner, Composing, Glossary, Infrastructure, PNG
		PNG (Portable Network Graphics) is a graphics file format that supports lossless data compression.
245	POP3	Beginner, Glossary, Infrastructure
		POP3 (Post Office Protocol) is a very common protocol for getting emails from a mail server over a glossary("TCP"} connection. POP3 does not support folders, unlike the more recent IMAP4, which is harder to implement because of its more complex structure.
246	Parameter	CodingScripting, Glossary, JavaScript
		A parameter is a named variable passed into a function. Parameter variables are used to import arguments into functions.
247	Parent object	CodingScripting, Glossary, NeedsContent
		The object to which a given property or method belongs.
248	Parse	CodingScripting, Glossary, JavaScript
		Parsing means analyzing and converting a program into an internal format that a runtime environment can actually run, for example the JavaScript engine inside browsers.
249	Parser	CodingScripting, Glossary, glossary
		A parser is the module of a compiler or interpreter that parses a source code file.
250	Percent-encoding	Glossary, WebMechanics, glossary
		Percent-encoding is a mechanism to encode 8-bit characters that have specific meaning in the context of URLs. It is sometimes called URL encoding. The encoding consists of substitution: A '%' followed by the hexadecimal representation of the ASCII value of the replace character.
251	Pixel	Design, Glossary, Graphics, glossary
		A pixel is the smallest building block of a graphical display like a computer screen.
252	Placeholder names	Cryptography, Glossary, Security
		Placeholder names are commonly used in cryptography to indicate the participants in a conversation, without resorting to terminology such as "Party A," "eavesdropper," and "malicious attacker."
253	Plaintext	Cryptography, Glossary, Security
		Plaintext refers to information that is being used as an input to an encryption algorithm, or to ciphertext that has been decrypted.
254	Polyfill	CodingScripting, Glossary
		A polyfill is a piece of code (usually JavaScript on the Web) used to provide modern functionality on older browsers that do not natively support it.
255	Polymorphism	CodingScripting, Glossary
		Polymorphism is the presentation of one interface for multiple data types. For example, integers, floats, and doubles are implicitly polymorphic: regardless of their different types, they can all be added, subtracted, multiplied, and so on.
256	Port	Glossary, Intro, Port, Security, computer network, glossary, port
		For a computer connected to a network with an IP address, a port is a communication endpoint. Ports are designated by numbers, and below 1024 each port is associated by default with a specific protocol.
257	Preflight request	CORS, HTTP
		A CORS preflight request is a CORS request that checks to see if the CORS protocol is understood.
258	Presto	Glossary, Infrastructure, glossary
		Presto was the proprietary browser layout engine used to power the Opera browser until version 15. Since then, the Opera browser is based on Chromium, which uses the Blink layout engine.
259	Primitive	CodingScripting, Glossary, JavaScript
		A primitive (primitive value, primitive data type) is data that is not an object and has no methods. In JavaScript, there are 6 primitive data types: string, number, boolean, null, undefined, symbol (new in ECMAScript 2015).
260	Privileged	Glossary, Security
		Users are said to be privileged when they are granted additional rights to a system, or given ultimate access to content in a higher priority level when compared to normal users.
261	Progressive Enhancement	Accessibility, Design, Glossary
		Progressive enhancement is a design philosophy that centers around providing a baseline of essential content and functionality to as many users as possible, while at the same time going further and delivering the best possible experience only to users of the most modern browsers that can run all the required code.
262	Progressive web apps	Composing, Glossary, Progressive web apps
		Progressive web apps is a term used to describe the modern state of web app development. This involves taking standard web sites/apps that enjoy all the best parts of the Web — such as discoverability via search engines, being linkable via URLs, and working across multiple form factors — and supercharging them with modern APIs (such as Service Workers and Push) and features that confer other benefits more commonly attributed to native apps.
263	Property	Disambiguation, Glossary
		The term property can have several meanings depending on the context. It may refer to:
264	Property (CSS)	CodingScripting, Glossary
		A CSS property is a characteristic (like color) whose associated value defines one aspect of how the browser should display the element.
265	Property (JavaScript)	CodingScripting, Glossary, glossary
		A property is a characteristic of an object, often describing attributes associated with a data structure. There are two kinds of properties:
266	Protocol	Glossary, Infrastructure, Protocols
		A protocol is a system of rules that define how data is exchanged within or between computers.  Communications between devices require that the devices agree on the format of the data that is being exchanged. The set of rules that defines a format is called a protocol.
267	Prototype	Apps, Composing, Glossary
		Editorial review completed.
268	Prototype-based programming	CodingScripting, Glossary
		Prototype-based programming is a style of object-oriented programming in which classes are not explicitly defined, but rather derived by adding properties and methods to an instance of another class or, less frequently, add them to an empty object. In simple words, this type of style allows creating an object. without defining its class.
269	Proxy server	Glossary, Proxy, Server
		A proxy server is an intermediate program or computer used when navigating through different networks of the Internet. They facilitate access to content on the World Wide Web. A proxy intercepts requests and serves back responses; it may forward the requests, or not (for example in the case of a cache), and it may modify it (for example changing its headers, at the boundary between two networks).
270	Pseudo-class	CSS, CodingScripting, Glossary, Selector
		Technical review completed.
271	Pseudo-element	CSS, CodingScripting, Glossary, glossary
		In CSS, a pseudo-element selector applies styles to parts of your document content in scenarios where there isn't a specific HTML element to select. For example, rather than putting the first letter of each paragraph in its own element, you can style them all with p::first-letter.
272	Pseudocode	CodingScripting, Glossary, Pseudocode, glossary
		Pseudocode refers to code-like syntax that is generally used to indicate to humans how some code syntax works, or illustrate the design of an item of code architecture. It won't work if you try to run it as code.
273	Python	CodingScripting, Glossary, Language, Python, programming
		Python is a high level general-purpose programming language. It uses a multi-paradigm approach, meaning it supports procedural, object-oriented and some functional programming constructs.
274	Quality values	Glossary, WebMechanics
		Quality values, or q-values and q-factors, are used to describe the order of priority of values in a comma-separated list. It is a special syntax allowed in some HTTP headers and in HTML.
275	RDF	CodingScripting, Glossary, Infrastructure, OpenPractices, WebMechanics
		RDF (Resource Description Framework) is a language developed by W3C for representing information on the World Wide Web, such as Webpages. RDF provides a standard way of encoding resource information so that it can be exchanged in a fully automated way between applications.
276	REST	Glossary, Rest, WebMechanics
		Representational State Transfer (REST) refers to a group of software architecture design constraints that bring about efficient, reliable, and scalable systems.
277	RGB	Beginner, CSS, Design, Guide
		Technical review completed.
278	RIL	Firefox OS, Glossary, Infrastructure, Intro, Mobile, Telephony
		RIL (Radio Interface Layer) is a mobile operating system component which communicates between the device's software and the device's phone, radio, or modem hardware.
279	RSS	Glossary, OpenPractices, RSS, Sharing, WebMechanics
		RSS (Really Simple Syndication) refers to several XML document formats designed for publishing site updates. When you subscribe to a website's RSS feed, the website sends information and updates to your RSS reader in an RSS document called a feed, so you don't need to check all your favorite websites manually.
280	RTF	Composing, Format, Glossary, RTF, Rich Text Format
		RTF (Rich Text Format) is a plain-text-based file format with support for formatting instructions (like bold or italic).
281	Random Number Generator	CodingScripting, Glossary
		A PRNG (pseudorandom number generator) is an algorithm that outputs numbers in a complex, seemingly unpredictable pattern. Truly random numbers (say, from a radioactive source) are utterly unpredictable, whereas all algorithms are predictable, and a PRNG returns the same numbers when passed the same starting parameters or seed.
282	Raptor	CodingScripting, Glossary
		Raptor: New Performance Tools for Gaia
283	Raster image
		A raster image is an image file defined as a grid of pixels. They’re also referred to as bitmaps. Common raster image formats on the Web are JPEG, PNG, GIF, and ICO.
284	Recursion	CodingScripting, Glossary
		An act of a function calling itself. Recursion is used to solve problems that contain smaller sub-problems. A recursive function can receive two inputs: a base case (ends recursion) or a recursive case (continues recursion).
285	Reference	CodingScripting, Glossary, NeedsContent, glossary
		In the context of objects, this is an object reference. On MDN, we could be talking about the JavaScript reference itself.
286	Reflow	Glossary, WebMechanics
		Reflow happens when a browser must process and draw part or all of a webpage again, such as after an update on an interactive site.
287	Regular expression	CodingScripting, Glossary, Regular Expression
		Regular expressions (or regex) are rules that govern which sequences of characters come up in a search.
288	Rendering engine	Glossary, Infrastructure, Rendering engine, Web browser engine
		A rendering engine is software that draws text and images on the screen. The engine draws structured text from a document (often HTML), and formats it properly based on the given style declarations (often given in CSS). Examples of layout engines: Blink, Gecko, Edge, WebKit.
289	Repo	Glossary, Infrastructure, Intro, Repo, Repository
		No summary!
290	Reporting directive	CSP, HTTP, Security
		CSP reporting directives are used in a Content-Security-Policy header and control the reporting process of CSP violations.
291	Request header	Glossary, WebMechanics, glossary
		A request header is an HTTP header that can be used in an HTTP request, and that doesn't relate to the content of the message. Request headers, like Accept, Accept-*, or If-* allow to perform conditional requests; others like Cookie, User-Agent or Referer precise the context so that the server can tailor the answer.
292	Response header	Glossary, WebMechanics
		A response header is an HTTP header that can be used in an HTTP response and that doesn't relate to the content of the message. Response headers, like Age, Location or Server are used to give a more detailed context of the response.
293	Responsive web design	Accessibility, Design, Glossary, Responsive web design
		Responsive Web Design (RWD) is a Web development concept focusing on making sites look and behave optimally on all personal computing devices, from desktop to mobile.
294	Robots.txt	Glossary, Infrastructure
		Robots.txt is a file which is usually placed in the root of any website. It decides whether crawlers are permitted or forbidden access to the web site.
295	Ruby	CodingScripting, Glossary, Ruby
		Ruby is an open-source programming language. In a Web context, Ruby is often used server-side with the Ruby On Rails (ROR) framework to produce websites/apps.
296	SCM	CodingScripting, Glossary, SCM
		SCM (Source Control Management) is a system for managing source code. Usually it refers to the use of software to handle versioning of source files. A programmer can modify source code files without being afraid of editing out useful stuff, because a SCM keeps track of how the source code has changed and who made the changes.
297	SCTP	Glossary, Infrastructure, SCTP, WebRTC, glossary
		SCTP (Stream Control Transmission Protocol) is an IETF standard for a transport protocol which enables the reliable, in-order transmission of messages while offering congestion control, multi-homing, and other features to improve reliability and stability of the connection. It's used for sending traditional telephone calls over the Internet, but is also used for WebRTC data.
298	SDP	Advanced, Collaborating, Glossary, Infrastructure, Protocol, WebRTC
		SDP (Session Description Protocol) is the standard describing a peer-to-peer connection. SDP contains the codec, source address, and timing information of audio and video.
299	SEO	Glossary, Intro, SEO, Search, WebMechanic, open
		SEO (Search Engine Optimization) is the process of making a website more visible in search results, also termed improving search rankings.
300	SGML	CodingScripting, Composing, Glossary, SGML
		The Standard Generalized Markup Language (SGML) is an ISO specification for defining declarative markup languages.
301	SIMD	CodingScripting, Glossary, JavaScript
		SIMD (pronounced "seem-dee") is short for Single Instruction/Multiple Data which is one classification of computer architectures. SIMD allows one same operation to be performed on multiple data points resulting in data level parallelism and thus performance gains, for example for 3D graphics and video processing, physics simulations or cryptography, and other domains.
302	SISD	CodingScripting, Glossary
		SISD is short for Single Instruction/Single Data which is one classification of computer architectures. In SISD architecture, a single processor executes a single instruction and operates on a single data point in memory.
303	SLD	Glossary, Infrastructure
		An SLD (Second Level Domain) is a domain that is hierarchically directly below a TLD.
304	SMTP	Beginner, Collaboration, Glossary, Infrastructure, Sharing
		SMTP (Simple Mail Transfer Protocol) is a protocol used to send a new email.  Like POP3 and NNTP, it is a state machine-driven protocol.
305	SOAP	Glossary, Infrastructure, SOAP, WebMechanics
		SOAP (Simple Object Access Protocol) is a protocol for transmitting data in XML format. Firefox removed support for SOAP in 2008.
306	SQL	CodingScripting, Database, Glossary, Sql
		SQL (Structured Query Language) is a descriptive computer language designed for updating, retrieving, and calculating data in table-based databases.
307	SQL Injection	Glossary, Security, Sql, Sql Injection, Webapp
		SQL injection takes advantage of Web apps that fail to validate user input. Hackers can maliciously pass SQL commands through the Web app for execution by a backend database.
308	SRI	CSP, Security
		Subresource Integrity (SRI) is a security feature that enables browsers to verify that files they fetch (for example, from a CDN) are delivered without unexpected manipulation. It works by allowing you to provide a cryptographic hash that a fetched file must match.
309	STUN	Glossary, Infrastructure, STUN, WebMechanics, WebRTC
		STUN (Session Traversal Utilities for NAT) is an auxiliary protocol for transmitting data around a NAT (Network Address Translator). STUN returns the IP address, port, and connectivity status of a networked computer behind a NAT.
310	SVG	Beginner, CodingScripting, Glossary, Graphics, SVG, l10n:priority
		Scalable Vector Graphics (SVG) is a 2D vector image format based on an XML syntax.
311	SVN	Collaborating, Glossary
		Apache Subversion (SVN) is a free source control management (SCM) system. It allows developers to keep a history of text and code modifications. Although SVN can also handle binary files, we do not recommend that you use it for such files.
312	Safe	Glossary, WebMechanics
		An HTTP method is safe if it doesn't alter the state of the server. In other words, a method is safe if it leads to a read-only operation. Several common HTTP methods are safe: GET, HEAD, or OPTIONS. All safe methods are also idempotent as well as some, but not all, unsafe methods like PUT, or DELETE.
313	Scope	CodingScripting, Glossary
		The current context of execution. The context in which values and expressions are "visible," or can be referenced. If a variable or other expression is not "in the current scope," then it is unavailable for use. Scopes can also be layered in a hierarchy, so that child scopes have access to parent scopes, but not vice versa.
314	Search engine	Definition, Glossary, Indexing, Search Engine, Searching, Web Crawling, WebMechanics, World Wide Web, details, google
		A search engine is a software system that collects information from the World Wide Web and presents it to users who are looking for specific information.
315	Second-level Domain	Glossary, Infrastructure
		An SLD (Second Level Domain) is a domain that is hierarchically directly below a TLD.
316	Selector (CSS)	CSS, CSS Selector, CodingScripting, Glossary, HTML, Selector
		A CSS selector is the part of the CSS rule that lets you target which element(s) get styled by the rule. For example:
317	Semantics	CodingScripting, Glossary, HTML, semantics
		In programing, Semantics refers to the meaning of a piece of code — for example "what effect does running that line of JavaScript have?", or "what purpose or role does that HTML element have" (rather than "what does it look like?".)
318	Serialize	CodingScripting, Glossary, JavaScript, Serialize
		Serialization means to translate an object or some other kind of data structure into a storable format (like e.g. a file or a buffer).
319	Server	Glossary, Infrastructure, Networking, Protocol, Server
		A hardware server is a shared computer on a network that provides services to clients.  A software server is a program that provides services to client programs.
320	Session Hijacking	Glossary, Security, session hijacking
		Session hijacking occurs when an attacker takes over a valid session between two computers. The attacker steals a valid session ID in order to break into the system and snoop data.
321	Shim	CodingScripting, Glossary
		A shim is a piece of code used to correct the behavior of code that already exists, usually by adding new API that works around the problem. This differs from a polyfill, which implements a new API that is not supported by the stock browser as shipped.
322	Signature	Disambiguation, Glossary
		The term signature can have several meanings depending on the context. It may refer to:
323	Signature (functions)	CodingScripting, Glossary, Java, JavaScript
		A function signature (or type signature, or method signature) defines input and output of functions or methods.
324	Signature (security)	Cryptography, Glossary, Privacy, Security
		A signature, or digital signature, is a protocol showing that a message is authentic.
325	Simple header	CORS, Glossary, HTTP, Infrastructure
		A simple header (or CORS-safelisted request header) is one of the following HTTP headers:
326	Simple response header	CORS, Glossary, HTTP
		A simple response header (or a CORS-safelisted response header) is an HTTP header which has been safelisted so that it will not be filtered when responses are processed by CORS, since they're considered safe (as the headers listed in Access-Control-Expose-Headers).
327	Sloppy mode	CodingScripting, Glossary, JavaScript, Sloppy
		ECMAScript 5 and later let scripts opt in to a new strict mode, which alters the semantics of JavaScript in several ways to improve its resiliency and which make it easier to understand what's going on when there are problems.
328	Slug	Community, Glossary, Intermediate, MDN, URL, Web
		A Slug is the unique identifying part of a web address, typically at the end of the URL. In the context of MDN, it is the portion of the URL following "<locale>/docs/".
329	Smoke Test	Composing, Glossary, Intro, QA, Testing
		A smoke test consists of functional or unit tests of critical software functionality. Smoke testing comes before further, in-depth testing.
330	Specification	Glossary, OpenPractices, Standardization
		A specification is a document that lays out in detail what functionality or attributes a product must include before delivery. In the context of describing the Web, the term "specification" (often shortened to simply "spec") generally means a document describing a language, technology, or API which makes up the complete set of open Web technologies.
331	Stacking context	CSS, CodingScripting, Glossary
		Stacking context refers to how elements on a webpage appear to sit on top of other elements, just as you can arrange index cards on your desk to lie side-by-side or overlap each other.
332	State machine	CodingScripting, Finite, Glossary, Input, Mealy, Moore, State Machine, Turing Machine
		A state machine is a mathematical abstraction used to design algorithms. A state machine reads a set of inputs and changes to a different state based on those inputs.
333	Statement	Beginner, CodingScripting, Glossary
		Technical review completed.
334	Static typing	CodingScripting, Glossary, Type
		A statically-typed language is a language (such as Java, C, or C++) where variable types are known at compile time. In most of these languages, types must be expressly indicated by the programmer; in other cases (such as OCaml), type inference allows the programmer to not indicate their variable types.
335	String	Beginner, CodingScripting, Glossary, String
		In any computer programming language, a string is a sequence of characters used to represent text.
336	Symbol	ECMAScript 2015, Glossary, JavaScript, Sharing
		This glossary page describes both a data type, called "symbol", and the class-like function, called "Symbol()", that (among other things) creates instances of the symbol data type.
337	Synchronous	Glossary, Web, WebMechanics
		Synchronous refers to real-time communication where each party receives (and if necessary, processes and replies to) messages instantly (or as near to instantly as possible).
338	Syntax	CodingScripting, Glossary
		Syntax specifies the required combination and sequence of characters making up correctly structured code. Syntax varies from language to language (e.g., syntax is different in HTML and JavaScript). Syntax applies both to programming languages (commands to the computer) and markup languages (document structure information).
339	Syntax error	CodingScripting, Glossary, JavaScript
		An exception caused by the incorrect use of a pre-defined syntax. Syntax errors are detected while compiling or parsing source code.
340	TCP	Glossary, Infrastructure, Networking, TCP, Transmission Control Protocol, data
		TCP (Transmission Control Protocol) is an important network protocol that lets two hosts connect and exchange data streams.  TCP guarantees the delivery of data and packets in the same order as they were sent.  Vint Cerf and Bob Kahn, who were DARPA scientists at the time, designed TCP in the 1970s.
341	TLD	Glossary, Web, WebMechanics
		A TLD (top-level domain) is the most generic domain in the Internet's hierarchical DNS (domain name system). A TLD is the final component of a domain name, for example, "org" in developer.mozilla.org.
342	TLS	Cryptography, Glossary, Infrastructure, Security
		Transport Layer Security (TLS), previously known as Secure Sockets Layer (SSL), is a protocol used by applications to communicate securely across a network, preventing tampering with and eavesdropping on email, web browsing, messaging, and other protocols.
343	TOFU	HTTP, SSH, Security
		Trust On First Use (TOFU) is a security model in which a client needs to create a trust relationship with an unknown server. To do that, clients will look for identifiers (for example public keys) stored locally. If an identifier is found, the client can establish the connection. If no identifier is found, the client can prompt the user to to determine if the client should trust the identifier.
344	TTL	Caching, Domain Name System, Glossary, Infrastructure, Networking, Performance
		TTL can refer either to :
345	TURN	Glossary, Infrastructure, TURN, WebMechanics, WebRTC
		TURN (Traversal Using Relays around NAT) is a protocol enabling a computer to receive and send data from behind a Network Address Translator (NAT) or firewall.
346	Tag	CodingScripting, Glossary, HTML, Intro
		In HTML a tag is used for creating an element.  The name of an HTML element is the name used in angle brackets such as <p> for paragraph.  Note that the end tag's name is preceded by a slash character, "</p>", and that in empty elements the end tag is neither required nor allowed. If attributes are not mentioned, default values are used in each case.
347	Telnet	Glossary, Infrastructure
		Telnet is a command line tool and an underlying TCP/IP protocol for accessing remote computers.
348	Three js	Browser, CodingScripting, JavaScript, Programming Language, three.js
		three.js is a JavaScript-based WebGL engine that can run GPU-powered games and other graphics-powered apps straight from the browser. The three.js library provides many features and APIs for drawing 3D scenes in your browser.
349	Trident	Browser, Glossary, Infrastructure, Trident
		Trident (or MSHTML) was a layout engine that powered Internet Explorer. A Trident fork called EdgeHTML replaced Trident in Internet Explorer's successor, Edge.
350	Truthy	CodingScripting, Glossary, JavaScript
		Technical review completed.
351	Type	CodingScripting, Glossary, JavaScript
		Type  (or data type) is a characteristic of a value affecting what kind of data it can store — for example in JavaScript a Boolean only holds true/false values, whereas a String holds text strings, a Number holds numbers of any kind, etc.
352	Type Conversion	CodingScripting, Glossary, Type casting, Type conversion
		Type conversion (or typecasting) means transfer of data from one data type to another. Implicit conversion happens when the compiler automatically assigns data types, but the source code can also explicitly require a conversion to take place.  Simple examples: given the instruction 5+2.0, the integer 5 is implicitly typecasted into floating point, but given the instruction Number("0x11"), the string "0x11" is explicitly typecasted as the number 17.
353	UDP	Glossary, Infrastructure, UDP
		UDP (User Datagram Protocol) is a long standing protocol used together with IP for sending data when transmission speed and efficiency matter more than security and reliability.
354	UI	Accessibility, Design, Glossary, glossary
		Technical review completed.
355	URI	Glossary, HTTP, Landing, Search, URI, URL
		A URI (Uniform Resource Identifier) is a string that refers to a resource. The most common are URLs, which identify the resource by giving its location on the Web. URNs, by contrast, refer to a resource by a name, in a given namespace, e.g. the ISBN of a book.
356	URL	Glossary, Infrastructure, l10n:priority
		Uniform Resource Locator (URL) is a text string specifying where a resource can be found on the Internet.
357	URN	Glossary, Intro, Navigation, urn
		URN (Uniform Resource Name) is a URI in a standard format, referring to a resource without specifying its location or whether it exists. This example comes from RFC3986: urn:oasis:names:specification:docbook:dtd:xml:4.1.2
358	UTF-8	CodingScripting, Glossary, HTML, JavaScript, Utf-8
		UTF-8 (UCS Transformation Format 8) is the World Wide Web's most common character encoding. Each character is represented by one to four bytes. UTF-8 is backward-compatible with ASCII and can represent any standard Unicode character.
359	UX	Accessibility, Composing, Design, Glossary, Navigation
		UX is an acronym that stands for User eXperience. It is the study of the interaction between users and a system. Its goal is to make a system easy to interact with from the user's point of view.
360	Unicode	Infrastructure
		Unicode is a standard character set that numbers and defines characters from the world's different languages, writing systems, and symbols.
361	Usenet	Glossary, WebMechanics
		Usenet is an internet discussion system where each post is duplicated on many servers. The equivalent of Internet forums in its day, Usenet functioned like a bulletin board system.
362	User agent	Glossary, User-agent, WebMechanics, user agent
		A user agent is a computer program representing a person, for example, a browser in a Web context.
363	Validator	Beginner, Glossary, Security
		A validator is a program that checks for syntax errors in code. Validators can be created for any format or language, but in our context we speak of tools that check HTML, CSS, and XML.
364	Value	CodingScripting, Glossary, NeedsContent
		Technical review completed.
365	Variable	CodingScripting, JavaScript
		A variable is a named location for storing a value. That way an unpredictable value can be accessed through a predetermined name.
366	Vendor Prefix	CodingScripting, Glossary
		Browser vendors sometimes add prefixes to experimental or nonstandard CSS properties and JavaScript APIs, so developers can experiment with new ideas while—in theory—preventing their experiments from being relied upon and then breaking web developers' code during the standardization process. Developers should wait to include the unprefixed property until browser behavior is standardized.
367	Viewport	CodingScripting, Glossary
		A viewport represents a polygonal (normally rectangular) area in computer graphics that is currently being viewed. In web browser terms, it refers to the part of the document you're viewing which is currently visible in its window. Content outside the viewport is currently not displayed onscreen.
368	VoIP	Glossary, Infrastructure, VoIP
		VoIP (Voice over Internet Protocol) is a technology used to transmit voice messages over IP (Internet Protocol) networks. Common VoIP packages include Skype, Msn Messenger, Yahoo and many more. Everything transferrred through VoIP is digital. It is also known as IP telephony, or broadband telephony. The main reason for using VoIP technology is because of cost.
369	W3C	Community, Consortium, Glossary, Intro, W3C, Web consortium
		The World Wide Web Consortium (W3C) is an international body that maintains Web-related rules and frameworks.
370	WAI	Accessibility, Glossary
		WAI or Web Accessibility Initiative is an effort by the World Wide Web Consortium (W3C) to improve accessibility for people with various challenges, who may need a nonstandard browser or devices.
371	WCAG	Accessibility, Glossary, WCAG, Web Guidelines
		Web Content Accessibility Guidelines (WCAG) are a recommendation published by the Web Accessibility Initiative group at the W3C. They outline a set of guidelines for making content accessible primarily for people with disabilities but also for limited-resource devices such as mobile phones.
372	WHATWG	Community, Glossary, HTML, HTML5, WHATWG, Web
		The WHATWG (Web Hypertext Application Technology Working Group) is an organization that maintains and develops HTML and APIs for Web applications. Former employees of Apple, Mozilla, and Opera established WHATWG in 2004.
373	Web standards	Glossary, Infrastructure, Web Standards, glossary, standards, web specifications
		Web standards are rules established by international standards bodies and defining how how the Web works (and sometimes controlling the Internet as well).
374	WebDAV	Glossary, Infrastructure
		WebDAV (Web Distributed Authoring and Versioning) is an HTTP Extension that lets web developers update their content remotely from a client.
375	WebExtensions	CodingScripting, Glossary, NeedsContent, WebExtensions
		WebExtensions is a cross-browser system for developing browser extensions in Firefox. This system provides APIs, which to a large extent are supported across different browsers like Mozilla Firefox, Google Chrome, Opera Browser, and Microsoft Edge .
376	WebGL	Advanced, CodingScripting, Glossary, Web Graphics, WebGL
		WebGL (Web Graphics Library) is a JavaScript API that draws interactive 2D and 3D graphics.
377	WebIDL	CodingScripting, Glossary, WebIDL, glossary
		WebIDL is the interface description language used to describe the data types, interfaces, methods, properties, and other components which make up a Web application programming interface (API). It uses a somewhat stylized syntax which is independent of any specific programming language, so that the underlying code which is used to build each API can be written in whatever language is most appropriate, while still being possible to map the API's components to JavaScript-compatible constructs.
378	WebKit	Browser, Glossary, Intro, Web, WebKit, WebMechanics
		WebKit is a framework that displays properly-formatted webpages based on their markup. Apple Safari depends on WebKit, and so do many mobile browsers (since WebKit is highly portable and customizable).
379	WebM	Composing, Glossary, Infrastructure, WebM
		WebM is royalty-free and is an open web video format natively supported in Mozilla Firefox.
380	WebP	Beginner, Composing, Glossary, Infrastructure, WebP
		WebP is a lossless and lossy compression image format developed by Google.
381	WebRTC	CodingScripting, Glossary, Infrastructure, JavaScript, P2P, VoIP, Web, WebRTC
		WebRTC (Web Real-Time Communication) is an API that can be used by video-chat, voice-calling, and P2P-file-sharing Web apps.
382	WebSockets	Connection, Glossary, Infrastructure, Networking, Protocols, Web, WebSocket
		WebSocket is a protocol that allows for a persistent TCP connection between server and client so they can exchange data at any time.
383	WebVTT	Audio, CodingScripting, Glossary, Video, Web, WebVTT, audio, glossary, video
		WebVTT (Web Video Text Tracks) is a W3C specification for a file format marking up text track resources in combination with the HTML <track> element.
384	World Wide Web	Glossary, Infrastructure, WWW, World Wide Web
		The World Wide Web—commonly referred to as WWW, W3, or the Web—is an interconnected system of public webpages accessible through the Internet. The Web is not the same as the Internet: the Web is one of many applications built on top of the Internet.
385	Wrapper	CodingScripting, Glossary, Wrapper
		Technical review completed.
386	XForm	CodingScripting, Glossary, Obsolete, XForms
		Editorial review completed.
387	XHR (XMLHttpRequest)	API, Beginner, CodingScripting, Glossary, XMLHttpRequest
		XMLHttpRequest (XHR) is a JavaScript API to create AJAX requests. Its methods allow to send network requests between the browser and a server.
388	XHTML	CodingScripting, Glossary, XHTML, glossary
		Technical review completed.
389	XInclude	CodingScripting, Glossary, glossary
		XML Inclusions (XInclude) is a W3C Recommendation to allow inclusion of XML more different sources in a more convenient fashion than XML external entities. When used in conjunction with XPointer (Firefox supports a subset of it, and is used in the code sample below), XInclude can also target just specific portions of a document for inclusion. Firefox does not support it natively, but the following function aims to allow its use with documents passed into it.
390	XLink	CodingScripting, Glossary, glossary
		XLink is a W3C standard which is used to describe links between XML and XML or other documents. Some its behaviors are left to the implementation to determine how to handle.
391	XML	CodingScripting, Glossary, XML, l10n:priority
		eXtensible Markup Language (XML) is a generic markup language specified by the W3C. The information technology (IT) industry uses many languages based on XML as data-description languages.
392	XPath	CodingScripting, Glossary, XML, XPath, glossary
		XPath is a query language that can access sections and content in an XML document.
393	XQuery	CodingScripting, Glossary, XML, XQuery, glossary
		Editorial review completed.
394	XSLT	CodingScripting, Glossary, XML, XSLT
		eXtensible Stylesheet Language Transformations (XSLT) is a declarative language used to convert XML documents into other XML documents, HTML, PDF, plain text, and so on.
395	buffer	Buffer, CodingScripting, Glossary, NeedsContent
		A buffer is a storage in physical memory used to temporarily store data while it is being transferred from one place to another.
396	document environment	CodingScripting, Glossary, JavaScript
		When the JavaScript global environment is a window or an iframe, it is called a document environment.A global environment is an environment that doesn't have an outer environment.
397	firewall	DDoS, Firewall, Glossary, Security, computer network
		A firewall is a system that filters network traffic. It can either let it pass or block it, according to some specified rules. For example, it can block incoming connections aimed at a certain port or outgoing connections to a certain IP address.
398	jQuery	Glossary, JQuery, JavaScript
		jQuery is a JavaScript Library that focuses on simplifying DOM manipulation, AJAX calls, and Event handling. It is used by JavaScript developers frequently.
399	loop	CodingScripting, Glossary, control flow, programming
		A loop is a sequence of instructions that is continually repeated until a certain condition is met in computer programming. An example would be the process of getting an item of data and changing it, and then making sure some condition is checked such as, if a counter has reached a prescribed number.
400	ltr	Composing, Glossary, Localization
		Technical review completed.
401	mime	Beginner, Glossary, Infrastructure, MIME
		MIME Multipurpose internet mail extensions supports text in other forms beside ASCII and non-text attachments such as audio, video and images.
402	non-normative	Glossary, Infrastructure, Specification, Standardization
		Editorial review completed.
403	privileged code	privileged
		Privileged code - Javascript code of your extension. For example, code in content scripts.
404	rtl	Composing, Glossary, Localization
		Technical review completed.
405	undefined	CodingScripting, Glossary, NeedsContent
		A primitive value automatically assigned to variables that have just been declared or to formal arguments for which there are no actual arguments.