$braces = qr/(?<braces>\{ ([^\{\}] | (?&braces))*? \} )/x;
$brackets = qr/(?<brackets>\( ([^\(\)] | (?&brackets))*? \))/x;
$identifier = qr/(?<identifier> \w+($brackets)?( \s*(\.|->)(?&identifier))?)/;

##</code><code>##

#This works
$meth_impl =~ s/((?<identifier> \w+($brackets)?( \s*(\.|->)(?&identifier))?)) \s* \. \s* Trim\(\)/Trim($1)/xg; 

#This doesn't match anything:
$meth_impl =~ s/($identifier) \s* \. \s* Trim\(\)/Trim($1)/xg;