Allowed nesting of elements in HTML 4 (and XHTML 1.0)

Nesting rules for HTML 4.01 Transitional

HTML

• HEAD
  • TITLE (required)
  • SCRIPT, STYLE
    • CDATA
  • ISINDEX, BASE, META, LINK (empty)
  • OBJECT (see content model below)
• BODY
  • INS, DEL (special rules apply)
    • flow
  • flow
    • block
      • P, H1, H2, H3, H4, H5, H6
        • inline
      • UL, OL
        • LI
          • flow
      • DIR, MENU
        • LI
          • inline exluding block
      • DL
        • DT
          • inline
        • DD
          • flow
      • PRE
        • inline excluding IMG, OBJECT, APPLET, BIG, SMALL, SUB, SUP, FONT, BASEFONT
      • DIV, CENTER, BLOCKQUOTE, IFRAME
        • flow
      • NOSCRIPT
        • flow
      • NOFRAMES
        • flow
      • FORM
        • flow excluding an enclosed FORM
      • ISINDEX, HR (empty)
      • TABLE
        • CAPTION
          • inline
        • COLGROUP
          • COL (empty)
        • COL (empty)
        • THEAD, TBODY, TBODY
          • TR
            • TH, TD
              • flow
      • ADDRESS
        • inline
        • P
          • inline
      • FIELDSET
        • #PCDATA
        • flow
        • LEGEND
          • inline
    • inline
      • #PCDATA
      • TT, I, B, U, S, STRIKE, BIG, SMALL, FONT, EM, STRONG, DFN, CODE, SAMP, KBD, VAR, CITE, ABBR, ACRONYM, SUB, SUP, Q, SPAN, BDO
        • inline
      • A
        • inline excluding an enclosed A element
      • OBJECT, APPLET
        • PARAM (empty)
        • flow
      • IMG, BASEFONT, BR (empty)
      • SCRIPT
        • CDATA
      • MAP
        • AREA (empty)
        • block
      • INPUT (empty)
      • SELECT
        • OPTGROUP
          • OPTION
        • OPTION
      • TEXTAREA
      • LABEL
        • LABEL excluding enclosed LABEL
      • BUTTON
        • flow excluding A, INPUT, SELECT, TEXTAREA, LABEL, BUTTON, FORM, ISINDEX, FIELDSET, IFRAME

Nesting rules for HTML 4.01 Frameset

HTML

• HEAD (content model as above)
• FRAMESET
  • FRAMESET (note recursion)
  • FRAME (empty)
  • NOFRAMES
    • BODY (see content model above) excluding NOFRAMES

In HTML 4.01 Frameset, the content model for NOFRAMES applies inside the BODY too, instead of the content model for NOFRAMES in HTML 4.01 Transitional.

The information here is based on the DTDs, basically the transitional DTD, in the 1999-12-24 version of the HTML 4.01 Specification.

Note that XHTML 1.0 is, as its subtitle says, "A Reformulation of HTML 4 in XML 1.0", so the nesting rules are the same as in HTML 4.01. However, there are the following differences that affect the nesting rules:

• The content of script and style elements is CDATA in HTML 4 but #PCDATA in XHTML.
• In XHTML, a table element may have a tr element as its direct constituent. In HTML 4.01, that's not allowed, but note that since the start and end tags of a tbody element are omissible in HTML 4.01, this is not a big difference. However, note that when a table element directly contains a tr element, an intervening tbody element is implied by HTML 4.01 rules but not by XHTML rules, and this matters e.g. when you have a style sheet which uses tbody as a selector.

Moreover, some of the restrictions on nesting are expressed differently; due to metalanguage differences, some limitations are described in prose only in the XHTML specification, and this implies that a validator will not catch such violations of the limitations when validating against XHTML DOCTYPE but will catch them when an HTML DOCTYPE is used. See section Differences with HTML 4 in the XHTML 1.0 Specification.

Date of last update: 2001-04-06

Interested in related documents? See a list of documents about WWW written or recommended by me.

Specifically, this document has a sister: Allowed nesting of elements in HTML 4 Strict (and XHTML 1.0 Strict), which describes the rules for the Strict versions, which include all elements and attributes that have not been deprecated or do not appear in frameset documents.