Headings

HTML defines six levels of headings. A heading element implies all the font changes, paragraph breaks before and after, and any white space necessary to render the heading. The heading elements are H1, H2, H3, H4, H5, and H6 with H1 being the highest (or most important) level and H6 the least. For example:

<H1>This is a top level heading</H1> Here is some text.
<H2>Second level heading</H2> Here is some more text.

Use the DIV element together with header elements when you want to make the hierarchical structure of a document explicit. This is needed as header elements themselves only contain the text of the header, and do not imply any structural division of documents into sections. Header elements have the same content model as paragraphs, that is text and character level markup, such as character emphasis, inline images, form fields and math.

Headers play a related role to lists in structuring documents, and it is common to number headers or to include a graphic that acts like a bullet in lists. HTML 3.0 recognizes this with attributes that assist with numbering headers and allow authors to specify a custom graphic.

The numbering style is controlled by the style sheet, e.g.

1. The style sheet specifies whether headers are numbered, and which style is used to render the current sequence number, e.g. arabic, upper alpha, lower alpha, upper roman, lower roman or a numbering scheme appropriate to the current language.
2. Whether the parent numbering is inherited, e.g. "5.1.d" where 5 is the current sequence number for H1 headers, 1 is the number for H2 headers and 4 for H3 headers.

The seqnum and skip attributes can be used to override the default treatment of header sequence numbers, and provide for a continuity with numbered lists.

The dingbat or src attribute may be used to specify a bullet-like graphic to be placed adjacent to the header. The positioning of this graphic is controlled by the style sheet. The graphic is for decorative purposes only and silently ignored on non-graphical HTML user agents.

Word Wrapping

User agents are free to wrap lines at whitespace characters so as to ensure lines fit within the current window size. Use the &nbsp; entity for the non-breaking space character, when you want to make sure that a line isn't broken! Alternatively, use the NOWRAP attribute to disable word wrapping and the <BR> element to force line breaks where desired.

Netscape includes two tags: <NOBR>...</NOBR>, and <WBR>. The former turns off wordwrapping between the start and end NOBR tag, while WBR is for the rare case when you want to specify where to break the line if needed. Should HTML 3.0 provide an equivalent mechanism to WBR, (either a tag or an entity)?

Permitted Attributes

ID

An SGML identifier used as the target for hypertext links or for naming particular elements in associated style sheets. Identifiers are NAME tokens and must be unique within the scope of the current document.

LANG

This is one of the ISO standard language abbreviations, e.g. "en.uk" for the variation of English spoken in the United Kingdom. It can be used by parsers to select language specific choices for quotation marks, ligatures and hypenation rules etc. The language attribute is composed from the two letter language code from ISO 639, optionally followed by a period and a two letter country code from ISO 3166.

CLASS

This a space separated list of SGML NAME tokens and is used to subclass tag names. For instance, <H2 CLASS=Section> defines a level 2 header that acts as a section header. By convention, the class names are interpreted hierarchically, with the most general class on the left and the most specific on the right, where classes are separated by a period. The CLASS attribute is most commonly used to attach a different style to some element, but it is recommended that where practical class names should be picked on the basis of the element's semantics, as this will permit other uses, such as restricting search through documents by matching on element class names. The conventions for choosing class names are outside the scope of this specification.

ALIGN

Headings are usually rendered flush left. The ALIGN attribute can be used to explicitly specify the horizontal alignment:

align=left

The heading is rendered flush left (the default).

align=center

The heading is centered.

align=right

The heading is rendered flush right.

align=justify

Heading lines are justified where practical, otherwise this gives the same effect as the default align=left setting.

For example:

<h1 align=center>This is a centered heading</H1>
Here is some text. <H2 align=right>and this is a flush right
heading</H2> Here is some more text.

CLEAR

This attribute is common to all block-like elements. When text flows around a figure or table in the margin, you sometimes want to start an element like a header, paragraph or list below the figure rather than alongside it. The CLEAR attribute allows you to move down unconditionally:

clear=left

move down until left margin is clear

clear=right

move down until right margin is clear

clear=all

move down until both margins are clear

Alternatively, you can decide to place the element alongside the figure just so long as there is enough room. The minimum width needed is specified as:

clear="40 en"

move down until there is at least 40 en units free

clear="100 pixels"

move down until there is at least 100 pixels free

The style sheet (or browser defaults) may provide default minimum widths for each class of block-like elements.

SEQNUM

A sequence number is associated with each level of header from the top level (H1) to the bottom level (H6). This attribute is used to set the sequence number associated with the header level of the current element to a given number, e.g. SEQNUM=10. Normally, the sequence number is initialized to 1 at the beginning of the document and incremented after each header element. It is reset to 1 by any header element of a higher level, e.g. an H1 header resets the sequence numbers for H2 to H6. The style of header numbering is controlled by the style sheet.

SKIP

Increments the sequence number before rendering the element. It is used when headers have been left out of the sequence. For instance, SKIP=3 advances the sequence number past 3 omitted items.

DINGBAT

Specifies an iconic image to appear preceding the header. The icon is specified as an entity name. A list of standard icon entity names for HTML 3.0 is given in an appendix of this specification.

SRC

Specifies an image to appear preceding the header. The image is specified as a URI. This attribute may appear together with the MD attribute.

MD

Specifies a message digest or cryptographic checksum for the associated graphic specified by the SRC attribute. It is used when you want to be sure that a linked object is indeed the same one that the author intended, and hasn't been modified in any way. For instance, MD="md5:jV2OfH+nnXHU8bnkPAad/mSQlTDZ", which specifies an MD5 checksum encoded as a base64 character string. The MD attribute is generally allowed for all elements which support URI based links.

NOWRAP

The NOWRAP attribute is used when you don't want the browser to automatically wrap lines. You can then explicitly specify line breaks in headings using the BR element. For example:

<h1 nowrap>This heading has wordwrap turned off<br>
and the BR element is used for explicit line breaks</H1>