+=head1 DESCRIPTION
+
+As of perl 5.9.5 it's possible to lexically replace perl's built-in
+regular expression engine with your own (see L<perlreapi> and
+L<perlpragma>). This module provides a glue interface to the relevant
+parts of the perl C API enabling you to write an engine in Perl
+instead of the C/XS interface provided by the core.
+
+=head2 The gory details
+
+Each regex in perl is compiled into an internal C<REGEXP> structure
+(see L<perlreapi|perlreapi/The REGEXP structure>), this can happen
+either during compile time in the case of patterns in the format
+C</pattern/> or runtime for C<qr//> patterns, or something inbetween
+depending on variable interpolation etc.
+
+When this module is loaded into a scope it inserts a hook into
+C<$^H{regcomp}> (as described in L<perlreapi> and L<perlpragma>) to
+have each regexp constructed in its lexical scope handled by this
+engine, but it differs from other engines in that it also inserts
+other hooks into C<%^H> in the same scope that point to user-defined
+subroutines to use during compilation, execution etc, these are
+described in L</CALLBACKS> below.