n some paths
and not on others), is not supported.
</P>
<P>
5. Callouts are supported, but the value of the <i>capture_top</i> field is
always 1, and the value of the <i>capture_last</i> field is always 0.
</P>
<P>
6. The \C escape sequence, which (in the standard algorithm) always matches a
single code unit, even in a UTF mode, is not supported in UTF modes because
the alternative algorithm moves through the subject string one character (not
code unit) at a time, for all active paths through the tree.
</P>