W3's HTML 4.01 DTD uses "- -", "- o" and "o o" in ELEMENT entries between the element name and it's content model. For example:
<!ELEMENT P - o (%inline;)* -- paragraph -->
<!ELEMENT (%heading;) - - (%inline;)* -- heading -->
<!ELEMENT TBODY o o (TR)+ -- table body -->
I've searched the net and can't find any mention of them. And all the XML books I have don't have them. What are they and what do they mean?