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Dynamic HTML: The Definitive Reference, 2rd Ed.Dynamic HTML: The Definitive ReferenceSearch this book


absolute positioning
Setting the precise location of an element within the coordinate system of the next outermost container. An absolute-positioned element exists in its own transparent layer; it is removed from the flow of content that surrounds it in the HTML source code.

abstract object
A specification for the characteristics of other, real objects with which scripts come into contact. Modern document object model designers frequently blend the characteristics of multiple abstract objects into a single scriptable object. For example, the properties, methods, and event handlers for a specific HTML p element object in a document loaded into Netscape 6 are derived from many W3C DOM specification abstract objects: the Node, Element, HTMLElement, HTMLParagraphElement, ElementCSSInlineStyle, and EventTarget objects.

The design concern for allowing users with physical disabilities to make as full a use of web content as possible. For example, aural style sheets provide increased web accessibility to users who have vision impairments. See also WAI.

Application Programming Interface, which is usually a collection of methods and properties that operate as a convenient layer between programmers and more complex internal computer activity. In Dynamic HTML, it is common to use or create a custom API to act as a buffer between the browser-specific implementations of element positioning and the programmer's desire to use a single coding scheme regardless of browser.

A type of CSS command used inside a style sheet definition. Typical at-rule commands import external style sheets or download font specifications. An at-rule statement begins with the @ symbol.

A property of an HTML (and XHTML) element or CSS style sheet. Attributes are usually assigned values by way of operators (the = symbol for HTML; the : symbol for CSS). In HTML, sometimes the presence of the attribute name is enough to turn on a feature associated with that attribute (regardless of the value assigned), but XHTML requires that all attributes have values assigned to them. HTML attribute names are case-insensitive; XHTML and CSS attribute names are case-sensitive.

block-level element
An HTML element that automatically forces a new line before and after the element, assuring that no other element appears in the same horizontal band of the page (unless another element is absolute-positioned on top of it). An example of a block-level element is the h1 element.

In CSS, a region that exists outside of the content and padding area of a block-level element. The border is always present, even if its thickness is zero, and it can't be seen. A border is sandwiched between the margin and padding.

browser sniffing
A script technique (usually involving properties of the navigator object) that sets global variables signifying the current browser's brand, version, operating system, and other environment capabilities. Scripts use the variables to branch code execution to accommodate browser-specific syntax for operations to work across multiple, incompatible browsers. The technique is gradually being displaced by object detection.

cascading rule
One of the sequence of decisions that a CSS-equipped browser uses to determine which one of several possible overlapping style sheet rules applies to a given element. Each cascading rule assigns a value to a specificity rating that helps determine which style sheet rule (and attributes within that rule) applies to the element.

In CSS, a collection of one or more elements (of the same or different tag type) that are grouped together for the purpose of assigning the same style sheet rule throughout the document. Assigning a class identifier to elements via the class attribute (and using that class selector in a style sheet rule) lets authors create element groupings that cannot be created only out of tag names or IDs.

A group of scriptable objects of the same type. Scripts may reference individual members of the collection via standard numeric array index syntax (collectionName[index]), aided by the collection's length property for iterative access inside for loops, if desired. In recent browsers, methods allow access via numeric index (collectionName.item(index)) or, if the objects have names associated with them, their names (collectionName.namedItem("name")). Internet Explorer also allows references through its own collection notation (collectionName(index)). Many DOM properties and methods return values in the form of a collection.

Any element that holds other elements of any type. Tags for contained elements appear between the container's start and end tags.

contextual selector
In CSS, a way of specifying under what containment circumstances a particular type of element should have a style sheet rule applied to it. The containment hierarchy is denoted in the selector by a space-delimited list. Thus, the rule p em {color: red} applies the red text color to all em elements that are contained by p elements; an em element inside an li element is unaffected by this style sheet rule.

Acronym for Cascading Style Sheets, a recommended standard created under the auspices of the World Wide Web Consortium (W3C). The acronym is commonly followed by a number designating the version number of the standard. Level 2 of CSS is known as CSS2.

Acronym for Cascading Style Sheets-Positioning. Initially undertaken as an effort separate from the CSS work, the two standards come together in CSS2, and the CSS-P terminology is no longer needed.

data binding
A facility in Microsoft Internet Explorer that allows web page content to be dynamically linked to a data source, such as a server database. For example, a marquee element can grab the latest headlines from a database field as the page loads into the client and display those headlines as a scrolling tickertape. Windows versions have two-way access to many data source types, but IE for Macintosh's data binding works only with static tab- or comma-delimited text file sources.

In CSS, the combination of an attribute name, colon operator, and value assigned to the attribute. Multiple declarations in a single style sheet rule are separated by semicolons.

A web standard or language feature (commonly an HTML element or attribute and corresponding DOM equivalent) that is still supported in a standards release version, the use of which is discouraged in documents that support the version. A term that is deprecated in one version release is usually removed in the following release. Browser support for deprecated items usually continues for many generations for backward compatibility with existing documents that use the element or attribute.

Acronym for Dynamic Hypertext Markup Language. DHTML is an amalgam of several standards, including HTML (and XHTML), CSS, and DOM.

Acronym for the Document Object Model standards effort headed by the W3C. The term in all uppercase letters is commonly, but perhaps inappropriately, applied to a specific implementation of a document object model in a particular browser.

Acronym for the Document Type Definition, a document that defines in excruciating detail the types of elements, attributes, and attribute values that are permissible in an SGML (and thus HTML or XML) document. Users never see DTD documents, but they are commonly referenced within the <!DOCTYPE> element at the top of a document to define the markup rules followed by the document's content. Anyone may create a custom DTD for their documents, but most HTML documents adhere to one of the W3C-published DTDs.

dynamic content
Any HTML content that changes after the document has loaded. Content that does not require a reflow of the page can be accommodated in Navigator 3 and onward and Internet Explorer 4 and onward. The replaced img element is an example. IE 4 or later and Netscape 6 also allow body content to be changed after the document loads by automatically reflowing the page after the content changes.

A Switzerland-based standards body formerly known as the European Computer Manufacturers Association.

The common name for the JavaScript-based scripting language standard ECMA-262. The standard defines a core scripting language, without any specific references to web-based content. The functionality of the first edition of ECMA-262 is roughly equivalent to JavaScript 1.1 as deployed in Navigator 3. The second edition corrected errors of the first, while the third edition adds new features common to JavaScript 1.5.

Refers to a portion of a document that has a specific context within the document defined by an angle-bracketed tag or tag pair (start and end tag set). For example, the <body> tag creates a body element in the document.

event binding
A technique of instructing an object to process a particular event type when the event fires on that object.

event bubbling
The Internet Explorer 4 or later and Netscape 6 event model mechanism that propagates events from the target element upward through the HTML element hierarchy. After the event is processed (at the scripter's option) by the target element, event handlers higher up the hierarchy may perform further processing on the event. Event propagation can be halted at any point via the cancelBubble property or, in Netscape 6, the stopPropagation( ) method.

event handler
A script-oriented keyword that intercepts an event action (such as a mouse click) and initiates the execution of one or more script statements. An event handler can be specified as an attribute of an HTML element, assigned as a property of the scriptable object version of the element, or associated with the object through event model-specific methods (attachEvent( ) or addEventListener( )). Each element responds to a specific set of events.

event propagation
The process of event information coursing its way through the element or object hierarchy of a document. In recent browsers, an event propagates from the window, document, or body element (depending on the event type) inward toward the target element. At that point the event propagation performs a U-turn, and bubbles upward through the same container path. For an object to process an event as it passes toward the target element, the object must be set up to capture the event. Event bubbling is automatic for most event types.

A rendering feature of Internet Explorer 4 or later (for the Windows platform) that adds typographic effects to text content and animated transitions between views. A filter is assigned to an element by way of CSS syntax.

Acronym for Hypertext Markup Language, a simplified version of SGML tailored for content that is published across a network via the Hypertext Transfer Protocol (HTTP). Version 4 of the HTML standard (under the auspices of the W3C) extends the notion of separating content from form by letting HTML elements define the context of content, rather than its specific look. HTML is the foundation of XHTML.

An identifier for an element that should be unique among all elements within a single document. The ID of an element is assigned by the id attribute supported by every HTML 4 tag. An ID is used for many purposes, including associating a CSS style sheet rule with a single element among all elements of a document and simplifying script references to a specific element.

A name assigned to an id, class, or name attribute of an element, as well as names for objects and variables in a scripting language. The names can begin with any uppercase or lowercase letter of the English alphabet, but subsequent characters may include letters, numerals, or the underscore character.

inline element
An HTML element that is rendered as part of the same text line as its surrounding HTML content. An em element that signifies an emphasized portion of a paragraph is an inline element because its content does not disturb the regular linear flow of the content. The opposite of an inline element is a block-level element.

intrinsic events
Event handlers defined by the HTML 4 standard as belonging to virtually every element that is rendered on the page. These events are primarily the common mouse and keyboard events.

A programming language devised by Brendan Eich at Netscape for simplified server and client programming. Originally developed under the name LiveScript, the name changed (under license from Sun Microsystems) before the first commercial release of a scriptable browser, Navigator 2. JavaScript became the basis for ECMAScript. Microsoft's name for its implementation of JavaScript is JScript.

JavaScript Style Sheets
A Navigator 4-only syntax for defining style sheet rules.

Microsoft's formal name for the JavaScript-based scripting language built into Internet Explorer 3 and later. Compatible with ECMAScript and JavaScript.

Derived from Navigator 4's now-abandoned model for a positionable element, the term is currently a generic reference to any element with a CSS position attribute assigned a value such as absolute, relative, or fixed. Each positioned element exists in its own transparent layer above the main document body.

In CSS, a region that extends outside of an element's border. Every element has a margin, even if its thickness is zero.

In CSS, a reference to the type of output for which the rule is to be applied. Mainstream browsers commonly support the screen and print media, but the other possible media include projection, audio, and small screen displays of portable devices.

A scriptable object's action that can be initiated by any script statement. A reference to a JavaScript-syntax method is easily recognizable by the set of parentheses that follows the method name. Zero or more parameters may be included inside the parentheses. A method may return a value depending on what it has been programmed to do, but it isn't a requirement.

modifier key
A keyboard key that is usually pressed in concert with a character key or mouse action to initiate a special action. Modifier keys common to all operating system platforms include the Shift, Control, and Alt keys. Modern Microsoft keyboards also have the Windows key; Macintosh keyboards have the Command key. Keyboard and mouse events can be examined for which (if any) modifier keys were being held down at the time of the character key's event.

A tendency in recent W3C standards tracks to divide large standards into multiple modules, each of which has a specific focus, such as the Events module of the W3C DOM recommendation.

In a document object model, an object that can be referenced within the document's hierarchical structure. Some node types act as containers of additional, nested nodes, while other types contain nothing but document text content.

A representation of an HTML element or other programmable item in a scripting language, such as JavaScript. An object may have properties and methods that define the behavior and/or appearance of the object. Scripts typically read or modify object properties or invoke object methods to affect some change of value or appearance of the object. Objects in a browser's document object model reflect HTML elements defined by the document source code. For example, in recent browser versions, if a script assigns a new URL to the value of the src property of an img object, the new graphic replaces the old within the rectangular space occupied by the img element on the page. Other types of objects, such as dates and strings, do not appear on the screen directly but are used in script execution.

object detection
A scripting technique that verifies whether a browser supports a particular object, property, or method before attempting to execute a statement with that term in it. This technique is gaining favor over browser sniffing.

In CSS, a region that extends between the element's content and the border. Padding provides some breathing space between the content and a border (if one is specified). Every element has padding, even if its thickness is zero. Navigator 4 automatically adds visible padding to all positioned elements.

For HTML elements, the next outermost element in source code order (the tr element that surrounds a td element, for example). For positioned elements, the parent element determines the coordinate plane for an element's positioning. For scriptable window objects, a frame's parent is the frameset document that defines the frame holding the current document.

A software or hardware system that forms the basis for further product development. For web browsers, the term may apply to a browser brand (Netscape Navigator, Microsoft Internet Explorer, etc.) or the operating system on which a browser brand operates (Windows XP, Mac OS X, Solaris, etc.). In this book, platform usually applies to the browser brand.

Specifying the precise location of an element on the page. An element may be absolute-, relative-, or (in some browsers) fixed-positioned.

A single characteristic of an object, such as its ID or value, which can be retrieved (and sometimes set) with the help of scripting. Style sheet attributes are also sometimes referred to as properties because they can be scripted as properties of the style object.

A style sheet selector that points to a particular state or behavior of an HTML element, such as an a element set up as a link that has been visited recently by the user (a:visited).

A style sheet selector that points to a very specific piece of an element, such as the first letter of a paragraph (p:first-letter).

quirks (mode)
Reference to a mode whereby modern browsers emulate the nonstandard behaviors of their earlier versions for the sake of backward compatibility with existing HTML and CSS code. The operational mode (quirks versus standards-compatible modes) is controlled by settings in the <!DOCTYPE> tag for browsers such as IE 6 and Netscape 6.

relative positioning
Setting the precise location of an element within the coordinate system established by the location where the element would normally appear if it were not positioned. Documents preserve the blank space originally designated for a relative-positioned element so that surrounding content does not cinch up around the place left vacant by a positioned element.

replaced element
An inline or block-level element that can have its content replaced without requiring any adjustment of the document. An img element, for example, can have its content replaced by a script after the page has loaded.

An acronym for red-green-blue, the three base colors (in that order) for a popular color specification system, including those used for HTML and CSS color-related attributes. Values for each color are in the range between 0-255 (none to maximum saturation), in decimal or hexadecimal notation.

In CSS, a set of style declarations that are associated with one selector. A rule can also be embedded within an element as the value assigned to the style attribute of the element's tag.

In CSS, the name of the element(s), ID(s), class(es), or other permissible element groupings to which a style declaration is bound. The combination of a selector and declaration creates a style sheet rule.

style sheet
In CSS, one or more rules that define how a particular segment of document content should be rendered by the browser. A style sheet may be defined in an external document, in the style element, or assigned to an element via its style attribute.

In Internet Explorer for Windows, a visual effect for hiding and showing elements. Transitions are controlled via filters.

Passing source code through a program that compares the code against a standards-based measuring stick for syntactic accuracy, structural integrity, and adherence to standards requirements.

A scripting language alternate to JScript in Internet Explorer for Windows. You can combine script blocks in VBScript and JScript in the same document, and statements in each block may reference variables and objects in the other.

An acronym for the World Wide Web Consortium (http://www.w3.org).

An acronym for the Web Accessibility Initiative activity of the W3C; their goal is to promote web resources for users with disabilities (http://www.w3.org/WAI).

An acronym for the Extensible Hypertext Markup Language recommendation of the W3C. This branch of the HTML activity is a version of HTML implemented as an XML application (http://www.w3.org/MarkUp).

An acronym for the Extensible Markup Language recommendation of the W3C, which provides the basis for structuring data in a way that facilitates its storage and transfer around the Web (http://www.w3.org/XML).

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