XHTML 1.0 - Element Prohibitions

# B. Element Prohibitions

This appendix is normative.

The following elements have prohibitions on which elements they can contain (see SGML Exclusions). This prohibition applies to all depths of nesting, i.e. it contains all the descendant elements.

`a`
  must not contain other `a` elements.
`pre`
  must not contain the `img`, `object`, `big`, `small`, `sub`, or `sup` elements.
`button`
  must not contain the `input`, `select`, `textarea`, `label`, `button`, `form`, `fieldset`, `iframe` or `isindex` elements.
`label`
  must not contain other `label` elements.
`form`
  must not contain other `form` elements.