thm suffers from a number of disadvantages:
</P>
<P>
1. It is substantially slower than the standard algorithm. This is partly
because it has to search for all possible matches, but is also because it is
less susceptible to optimization.
</P>
<P>
2. Capturing parentheses and other features such as backreferences that rely on
them are not supported.
</P>
<P>
3. Matching within invalid UTF strings is not supported.
</P>
<P>
4. Although atomic groups are supported, their use does not provide the
performance ad