DTD explanation please

Hello There,

The following lines are from w3c.org, xhtml1 dtd file:

Code:

---

<!ELEMENT head (%head.misc;,
    ((title, %head.misc;, (base, %head.misc;)?) |
      (base, %head.misc;, (title, %head.misc;))))>
<!ELEMENT table
    (caption?, (col*|colgroup*), thead?, tfoot?, (tbody+|tr+))>

---

I am in the process of writing a DTD parser and am having a problem understanding those lines / finding any specification which properly describes how to interpret it.
What is the question mark for? What is the star for? What is the + for? Is there anybody out there having an idea how it supposed to work?

Thanks... :)