DB<114> $_='abc[de]'
 => "abc[de]"
 
  DB<115> $find='c[de]'
 => "c[de]"
 
  DB<116> $find2='c\[de\]'
 => "c\\[de\\]"
 
  DB<117> m/$find/             # no match
  DB<118> m/$find2/            # match
 => 1
  DB<119> m/\Q$find/           # match
 => 1
  DB<120> "\Q$find"            # how \Q=quotemeta works
 => "c\\[de\\]"