A DTD question

Is the HTML 4.01 DTD at www.w3.org supposed to be a valid DTD?

The element declarations in there are a bit unfamiliar. Here are two of them, for example:
<!ELEMENT HR - O EMPTY -- horizontal rule -->
<!ELEMENT Q - - (%inline;)* >

The problem areas are underlined. What do the "- -" and the "- O" mean and are they really supposed to be there?

Also, are there really supposed to be comments in the tag like that?

I don't know -- is there a difference between XML DTD and SGML DTD?

Avtually, I had already found out what the difference was and forgot about this thread.


Yeah, the HTML DTD at the w3c site is an SGML DTD and the DTD's we're all used to are XML DTD's. There are some differences. The XML DTD is simpler.