, and the second is user data that is supplied when the
function is set up. The callout function should return zero if all is well, or
non-zero to force an error. This feature is provided so that applications can
check the available system stack space, in order to avoid running out. The
result of <b>pcre2_set_compile_recursion_guard()</b> is always zero.
</P>
<P>
There is a complete description of the PCRE2 native API in the
<a href="pcre2api.html"><b>pcre2api</b></a>
page and a description of the POSIX API