>perl -wMstrict -le
"my $s = join '', @ARGV;
 $s = eval qq[qq[$s]];
 my $words = qr{ foo | bar }xms;
 $s =~ s{ (Kw \s+) (\"?) ($words) (\2 \s* \{) }{$1${2}1_$3$4}xmsg;
 print 'output:';
 print $s;
"
"Kw \n foo \n { \n Kw \n \"bar\"\n { \n Kw foo { Kw \"foo\" { "
"Kw \"foo { Kw foo\" { Kw foo Kw {"
output:
Kw
 1_foo
 {
 Kw
 "1_bar"
 {
 Kw 1_foo { Kw "1_foo" { Kw "foo { Kw foo" { Kw foo Kw {