If your text looks remotely like Perl, then Text::Balanced is worth a look. That module used to be part of the Parse::RecDescent distribution — it takes care of extracting the "Perl rules code" out of the grammars — but now it is a separate distribution.

#!/usr/bin/perl
use Text::Balanced 'extract_bracketed';

$_ = <<'#END#';
This stays

onValidate
   {
    stuff in here
    {
       other stuff
    }
   }

This stays too
#END#

if(/onValidate/) {
    print substr($_, 0, $-[0]);   # before
    my ($extracted, $remainder) = extract_bracketed(substr($_, $+[0]),
+ '{}');
    print $remainder;             # after
    print "\n## extracted: ##\n$extracted\n";
}
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which produces:

This stays



This stays too

## extracted: ##
{
    stuff in here
    {
       other stuff
    }
   }