In my self given task to make at least some UBB-templates correct xhtml I came across some errors that would be really easy to fix in ubb and would reduce the number of errors you have in UBB massively. Here is the top 3:
1. image tag. The img tag has a mandatory attribute alt. Add alt="" or sthg. to the UBB-Code converter. Change all occurences to xhtml (close the tag). <img src="xx" alt=""/>
2. Escape &. The '&' character has a special meaning. It marks is the start of an entity. This also applies within attributes. So a link with parameters should be escaped.
href="/xxx?bla=1&blu=2" is WRONG. Right way: href="/xxx?bla=1&blu=2". (This even applies to normal HTML)
3. Be careful with inline-elements. You are often using the <font> tag which is an inline-element. Inline (i.E. font, span, ...) elements are not allowed to contain block-level-elements. (I.E. table, p, ...) Surrounding a forum posting with an inline-element is not a good idea, since you normally can't be sure what will be inside the posting.
I believe the amount of errors will be reduced by about 90% if you fix these.
