TYPO3 Core

Also note that integer-only id's are not valid in XHTML 1.1 et al, so we cannot even have <a id="999">. My solution was to add a "c" in front of the tt_content uid:

1. Before each content object
   tt_content.stdWrap.dataWrap = <a id="c{field:uid}"></a> |

This might break a couple of other things that link to these internal links. One place that I have found is the cObj menu, type 3: "Section index (pagecontent w/Index checked)". A solution for that is:

tt_content.menu.20.3.renderObj.typolink.section.wrap = c |

IDs may never start with digit, neither in HTML nor XHTML.

Fixed.