August 2009

The SCRIPT element includes a client-side script in the document. Client-side scripts allow greater interactivity in a document by responding to user events. For example, a script could be used to check the user's form input prior to submission to provide immediate notice of any errors by the user.

The required TYPE attribute of SCRIPT specifies the media type of the scripting language, e.g., text/javascript. However, many browsers only support the deprecated LANGUAGE attribute, which specifies the language name. Examples of supported LANGUAGE values include JavaScript, JavaScript1.1, and VBScript. The values are not case sensitive.

An embedded script is given as the content of the SCRIPT element. The SRC attribute allows authors to reuse code by specifying an external script. The optional CHARSET attribute gives the character encoding of the external script, although this attribute is rarely needed in practice. When the SRC attribute is used, the embedded script is ignored. An example follows:

<SCRIPT TYPE="text/javascript" SRC="foo.js">
<!--
  // embedded script ignored
// -->
</SCRIPT>

Netscape 4.x requires that external scripts be served with a Content-Type of application/x-javascript.

The DEFER attribute indicates that the browser may wait to parse the script until the rest of the document has been rendered. Scripts that use DEFER must not generate any document content, and should not be required to respond to user events (e.g., form submission) that may occur while the document is loading. The DEFER attribute can be useful for delaying scripts that pre-load images or harass the user with scrolling messages in the status bar.

The SCRIPT element may occur any number of times in the document HEAD or BODY. Typically the SCRIPT element is used in the HEAD unless it generates BODY content.

Pre-HTML 3.2 browsers, unaware of the SCRIPT element, will treat the content of SCRIPT as normal HTML. To make these browsers ignore the SCRIPT's content, scripting languages generally allow SGML comments to be used around an embedded script. For example:

<SCRIPT TYPE="text/javascript">
<!-- comment to end of line
  document.write("foo");
// comment to end of line -->
</SCRIPT>

Note that "-->" is contained within a JavaScript single-line comment (started with two slashes).

Due to an unintuitive quirk of SGML, end tags are recognized within SCRIPT elements, but other kinds of markup--such as start tags and comments--are not. Almost all browsers ignore this rule, but authors should nonetheless avoid using strings such as "</P>" in their embedded scripts. JavaScript allows authors to use a backslash in the string to prevent it from being treated as an end tag, e.g., document.write("<\/P>").

The LINK element defines document relationships. Any number of LINK elements may be contained in the HEAD of a document. Many browsers lack support for LINK, so authors should not depend on the browser making the links available to the user.

The REL and REV attributes define the nature of the relationship between the documents and the linked resource. REL defines a link relationship from the current document to the linked resource while REV defines a relationship in the opposite direction. For example,

<LINK REL=Glossary HREF="foo.html">

indicates that foo.html is a glossary for the current document while

<LINK REV=Subsection HREF="bar.html">

indicates that the current document is a subsection of bar.html. The value of the REL and REV attributes is a space-separated list of link types.

Commonly used relationships include the next or previous document in a sequence, the starting page in a collection of documents, a document with copyright information, and information about the author. A document could define these relationships as follows:

<LINK REL=Prev HREF="base.html" TITLE="BASE - Document Base URI">
<LINK REL=Next HREF="meta.html" TITLE="META - Metadata">
<LINK REL=Start HREF="../" TITLE="HTML 4 Reference">
<LINK REL=Copyright HREF="/copyright.html" TITLE="Copyright Notice">
<LINK REV=Made HREF="mailto:liam@htmlhelp.com" TITLE="HTML 4 Reference Feedback">

While the value of REL and REV is case-insensitive, the Lynx browser renders the relationship exactly as given by the author. Authors should therefore be consistent in their case, and may wish to capitalize the first letter while using lowercase for the rest.

Authors can also use the LINK element to apply an external style sheet. REL=StyleSheet specifies a persistent or preferred style while REL="Alternate StyleSheet" defines an alternate style. A persistent style is one that is always applied when style sheets are enabled. The absence of the TITLE attribute indicates a persistent style.

A preferred style is one that is automatically applied. The combination of REL=StyleSheet and a TITLE attribute specifies a preferred style. Authors cannot specify more than one preferred style.

An alternate style is indicated by REL="Alternate StyleSheet". The user could choose to replace the preferred style sheet with an alternate one, though current browsers generally lack the ability to choose alternate styles.

A single style may also be given through multiple style sheets:

<LINK REL=StyleSheet HREF="basics.css" TITLE="Contemporary" TYPE="text/css">
<LINK REL=StyleSheet HREF="tables.css" TITLE="Contemporary" TYPE="text/css">
<LINK REL=StyleSheet HREF="forms.css" TITLE="Contemporary" TYPE="text/css">

In this example, three style sheets are combined into one "Contemporary" style that is applied as a preferred style sheet. To combine multiple style sheets into a single style, each style sheet's LINK must use the same TITLE.

LINK's MEDIA attribute specifies the media for which the linked resource is designed. With REL=StyleSheet, this allows authors to restrict a style sheet to certain output devices, such as printers or aural browsers. The attribute's value is a comma-separated list of media descriptors. The following media descriptors are defined in HTML 4 and are case-sensitive:

• screen, for non-paged computer screens;
• tty, for fixed-pitch character grid displays (such as the display used by Lynx);
• tv, for television-type devices with low resolution and limited scrollability;
• projection, for projectors;
• handheld, for handheld devices (characterized by a small display and limited bandwidth);
• print, for output to a printer;
• braille, for braille tactile feedback devices;
• aural, for speech synthesizers;
• all, for all devices.

Netscape 4.x incorrectly ignores any style sheet linked with a MEDIA value other than screen. For example, MEDIA="screen, projection" will cause the style sheet to be ignored by Netscape 4.x, even if the presentation device is a computer screen. Netscape 4.x also ignores style sheets declared with MEDIA=all.

The optional HREFLANG and CHARSET attributes of LINK give the language and character encoding, respectively, of the link. The language should be specified according to RFC 1766; examples include en for English, en-US for American English, and ja for Japanese. Examples of character encodings include ISO-8859-1, Shift_JIS, and UTF-8.

The Alternate link relationship defines an alternate version of the document. Translations of a page can be identified by using REL=Alternate along with the HREFLANG attribute. Versions of the page tailored for specific media can be provided by combining REL=Alternate with the MEDIA attribute. Some examples follow:

<LINK REL=Alternate HREF="index.fr.html" HREFLANG=fr LANG=fr TITLE="Version française">
<LINK REL=Alternate HREF="index.ja.html" HREFLANG=ja CHARSET="Shift_JIS" TITLE="Japanese version">
<LINK REL=Alternate HREF="/distribution/html40.pdf" TYPE="application/pdf" MEDIA=print TITLE="PDF version">

Note that the LANG and DIR attributes apply to the text of the TITLE attribute, not to the content of the link.

The BASE element defines the document's base URI for resolving relative URIs contained within the document. A document cannot contain more than one BASE element. When present, the BASE element must appear in the HEAD, prior to any elements that include a partial URI.

BASE's HREF attribute, required in HTML 4 Strict, specifies the absolute URI used to resolve relative URIs. See Using Relative URLs for more details on using and resolving relative URIs.

Most Web pages do not require an explicit base URI since the document's URI is a suitable base. An explicit base URI may be needed when the same document is available at different URIs or when the document has no URI (e.g., sending an HTML document by e-mail).

The BODY element contains the document body. BODY is required in non-frames documents, but its start and end tags are always optional. In frames documents, BODY must be contained within the NOFRAMES element, if NOFRAMES is used.

The BODY element contains the document's content. The content should be contained within block-level elements or SCRIPT elements, though HTML 4 Transitional also allows inline elements directly within BODY.

In addition to the core events common to most elements, BODY accepts the following event attributes for client-side scripting:

• ONLOAD, when the document has been loaded;
• ONUNLOAD, when the document is exited.