I answered a recent question about CSS psuedo elements with a reference to the document tree, or more specifically, document tree content.
http://www.w3.org/TR/CSS2/generate.html#before-after-content
…the:beforeand:afterpseudo-elements specify the location of content before and after an element’s document tree content.
The W3C’s explanation is very brief:
Document tree
The tree of elements encoded in the source document. Each element in this tree has exactly one parent, with the exception of the root element, which has none.
Although I’ve been searching for a more explicit reference as to what exactly this means, I can’t find anything useful. Can someone help explain exactly what document tree content is, and how to tell whether or not an HTML element has it?
I think it is referring to the hierarchal nature of HTML (elements having parents, siblings, children, ancestors, descendants, etc), and the content the child elements of the element of reference.