K escape sequence provide ways of
inspecting characters before the start of a matched string. The requirement for
inspecting at least one character exists because an empty string can always be
matched; without such a restriction there would always be a partial match of an
empty string at the end of the subject.
</P>
<P>
When a partial match is returned, the first two elements in the ovector point
to the portion of the subject that was matched, but the values in the rest of
the ovector are undefined. The app