#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;