Appendix A: Changes between HTML 3.2 and HTML 4.0

A.1 Changes to elements

A.1.1 New elements

The new elements in HTML 4.0 are: ABBR, ACRONYM, BDO, BUTTON, COLGROUP, DEL, FIELDSET, FRAME, FRAMESET, IFRAME, INS, LABEL, LEGEND, NOFRAMES, NOSCRIPT, OBJECT, OPTGROUP, PARAM, SPAN, TBODY, TFOOT, THEAD, and Q.

A.1.2 Deprecated elements

The following elements are deprecated: APPLET, BASEFONT, CENTER, DIR, FONT, ISINDEX, MENU, S, STRIKE, and U.

A.1.3 Obsolete elements

The following elements are obsolete: LISTING, PLAINTEXT, and XMP. For all of them, authors should use the PRE element instead.

A.2 Changes to attributes

• Almost all attributes that specify the presentation of an HTML document (e.g., colors, alignment, fonts, graphics, etc.) have been deprecated in favor of style sheets. The list of attributes in the appendix indicates which attributes have been deprecated.
• The id and class attribute allow authors to assign name and class information to elements for style sheets, as anchors, for scripting, for object declarations, general purpose document processing, etc.

A.3 Changes for accessibility

HTML 4.0 features many changes to promote accessibility, including:

• The title attribute may now be set on virtually every element.
• Authors may provide long descriptions of tables, images, and frames (see the longdesc attribute).

A.4 Changes for meta data

Authors may now specify profiles that provide explanations about meta specified with the META or LINK elements.

A.5 Changes for text

• New features for internationalization allow authors to specify text direction and language.
• The INS and DEL elements allow authors to mark up changes in their documents.
• The ABBR and ACRONYM elements allow authors to mark up abbreviations and acronyms in their documents.

A.6 Changes for links

• The id attribute makes any element the destination anchor of a link.

A.7 Changes for tables

The HTML 4.0 table model has grown out of early work on HTML+ and the initial draft of HTML3.0. The earlier model has been extended in response to requests from information providers as follows:

• Authors may specify tables that may be incrementally displayed as the user agent receives data.
• Authors may specify tables that are more accessible to users with non-visual user agents.
• Authors may specify tables with fixed headers and footers. User agents may take advantage of these when scrolling large tables or rendering tables to paged media.

The HTML 4.0 table model also satisfies requests for optional column-based defaults for alignment properties, more flexibility in specifying table frames and rules, and the ability to align on designated characters. It is expected, however, that style sheets will take over the task of rendering tables in the near future.

In addition, a major goal has been to provide backwards compatibility with the widely deployed Netscape implementation of tables. Another goal has been to simplify importing tables conforming to the SGML CALS model. The latest draft makes the align attribute compatible with the latest versions of the most popular browsers. Some clarifications have been made to the role of the dir attribute and recommended behavior when absolute and relative column widths are mixed.

A new element, COLGROUP, has been introduced to allow sets of columns to be grouped with different width and alignment properties specified by one or more COL elements. The semantics of COLGROUP have been clarified over previous drafts, and rules="basic" replaced by rules="groups".

The style attribute is included as a means for extending the properties associated with edges and interiors of groups of cells. For instance, the line style: dotted, double, thin/thick etc; the color/pattern fill for the interior; cell margins and font information. This will be the subject for a companion specification on style sheets.

The frame and rules attributes have been modified to avoid SGML name clashes with each other, and to avoid clashes with the align and valign attributes. These changes were additionally motivated by the desire to avoid future problems if this specification is extended to allow frame and rules attributes with other table elements.

A.8 Changes for images, objects, and image maps

• The OBJECT element allows generic inclusion of objects.
• The IFRAME and OBJECT elements allow authors to create embedded documents.
• The alt attribute is required on the IMG and AREA elements.
• The mechanism for creating image maps now allows authors to create more accessible image maps. The content model of the MAP element has changed for this reason.

A.9 Changes for forms

This specification introduces several new attributes and elements that affect forms:

• The accesskey attribute allows authors to specify direct keyboard access to form controls.
• The disabled attribute allows authors to make a form control initially insensitive.
• The readonly, allows authors to prohibit changes to a form control.
• The LABEL element associates a label with a particular form control.
• The FIELDSET element groups related fields together and, in association with the LEGEND element, can be used to name the group. Both of these new elements allow better rendering and better interactivity. Speech-based browsers can better describe the form and graphic browsers can make labels sensitive.
• A new set of attributes, in combination with scripts, allow form providers to verify user-entered data.
• The BUTTON element and INPUT with type set to "button" can be used in combination with scripts to create richer forms.
• The OPTGROUP element allows authors to group menu options together in a SELECT, which is particularly important for form accessibility.
• Additional changes for internationalization.

A.10 Changes for style sheets

HTML 4.0 supports a larger set of media descriptors so that authors may write device-sensitive style sheets.

A.11 Changes for frames

HTML 4.0 supports frame documents and inline frames.

A.12 Changes for scripting

Many elements now feature event attributes that may be coupled with scripts; the script is executed when the event occurs (e.g., when a document is loaded, when the mouse is clicked, etc.).

A.13 Changes for internationalization

HTML 4.0 integrates the recommendations of [RFC2070] for the internationalization of HTML.

However, this specification and [RFC2070] differ as follows:

• The accept-charset attribute has been specified for the FORM element rather than the TEXTAREA and INPUT elements.
• The HTML 4.0 specification makes additional clarifications with respect to the bidirectional algorithm.
• The use of CDATA to define the SCRIPT and STYLE elements does not preserve the ability to transcode documents, as described in section 2.1 of [RFC2070].