This function changes the detailing for all occurrences of the element named tagname in the document specified by doc. If doc is omitted or 0, the current document is used.

The expand parameter, if given and non-zero, causes the element and its contents to be displayed. If expand is omitted or 0, all occurrences of tagname are collapsed (detailed).

If tagname is a null string, detail_tag expands all elements in the document. In this case, the expand parameter is ignored.