s that no captured substrings are available.
</P>
<P>
3. Because no substrings are captured, a number of related features are not
available:
<br>
<br>
(a) Backreferences;
<br>
<br>
(b) Conditional expressions that use a backreference as the condition or test
for a specific group recursion;
<br>
<br>
(c) Script runs;
<br>
<br>
(d) Scan substring assertions.
</P>
<P>
4. Because many paths through the tree may be active, the \K escape sequence,
which resets the start of the match when encountered (but may be o