request: Need to be able to preview again after preview - I fixed some things but messed others ...

There's a very good reason for this. This page is written using the XHTML Strict DOCTYPE, and in this type of document (as in any other XHTML) all tags must be lowercase to be valid.

Of course, none of <b>, <i>, or <u>, are valid in XHTML Strict, and the author either forgot, did not realize, or did not care that many attributes in his XHTML don't escape ampersands, but nevertheless it is quite reasonable and justified for him to adhere to XHTML's requirement of lowercase tags.

It depends whether this site is people-oriented, or technique-oriented.

I think that this site is more people-oriented (am I wrong?)

If people make mistakes like that - it would be wise to handle it better - here are few possible ways to handle this problem.

One option: Have buttons that add the relevant tags - for example - select text and click the {BOLD} button will add the opening and closing tags around the selected text (I've seen this in another site)

Another option: is to allow people to review their text and correct it more than once.

And yet another: Check for such mixed case tags (using regular expressions) and fix them to lower case.