compatible with but not specified by IEEE Standard
1003.2 (POSIX.2), and should be used with caution in software intended to be
portable to other systems. Note that a non-zero <i>rm_so</i> does not imply
REG_NOTBOL; REG_STARTEND affects only the location and length of the string,
not how it is matched. Setting REG_STARTEND and passing <i>pmatch</i> as NULL
are mutually exclusive; the error REG_INVARG is returned.
</p>
<p>
If the pattern was compiled with the REG_NOSUB flag, no data about any matched
strings