> 1. Create the following 3 line file /tmp/x.html
 >
 > <table>
 >   <tr><td>'9'</td></tr>
 > </table>
 >
 > 2. invoke emacs -Q /tmp/x.html
 >
 > 3. C-x h   to mark the buffer
 >
 > 4. C-M-\   to indent the buffer
 >
 > 5. The indentation is not changed (correct), but the message
 >    Unclosed tag <>
 >    is generated (wrong).
 >
 > 6. This does not occur with emacs 22.2 and does not occur if
 >    the three characters '9' are replaced with 9 or '9 but does occur if
 >    they are replaced with 9'

This happens because `backward-sexp' calls `backward-prefix-chars' which
skips the "'".  Could you please try the attached patch.

Thank you, martin