Why can't I use "absbottom"?

My page is not Valid XHTML 1.0 Transitional because:

Line 70, Column 136: value of attribute “align” cannot be “absbottom”; must be one of “top”, “middle”, “bottom”, “left”, “right”.

Why can’t I use “absbottom”??

Also, I had:


But the validator says:

Line 74, Column 7: document type does not allow element “h3” here; missing one of “object”, “applet”, “map”, “iframe”, “button”, “ins”, “del” start-tag.

The mentioned element is not allowed to appear in the context in which you’ve placed it; the other mentioned elements are the only ones that are both allowed there and can contain the element mentioned. This might mean that you need a containing element, or possibly that you’ve forgotten to close a previous element.

One possible cause for this message is that you have attempted to put a block-level element (such as “<p>” or “<table>”) inside an inline element (such as “<a>”, “<span>”, or “<font>”).

What does that mean? Do I really have to remove either the <h3> or <dt> tag?