Following declaration appears in html 4.01 dtds
<!ELEMENT STYLE - - %StyleSheet -- style info -->
(see http://www.w3.org/TR/REC-html40/sgml/dtd.html it's in both strict.dtd and loose.dtd)
Apparently, the ; is missing after %StyleSheet. The reference should have been %StyleSheet;
But this is the official dtd of the holy html - by far the most important dtd of all dtds - so what's going on there? Is it valid entity reference like that?