use YAPE::Regex::Explain;
my $re = q{(?<!\\)(['"]).+?(?<!\\)(['"]};
print YAPE::Regex::Explain->new($re)->explain();

__END__

The regular expression:

(?-imsx:(?<!\)(['"]).+?(?<!\)(['"]))))

matches as follows:
  
NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  (?<!                     look behind to see if there is not:
----------------------------------------------------------------------
    \)                       ')'
----------------------------------------------------------------------
    (                        group and capture to \1:
----------------------------------------------------------------------
      ['"]                     any character of: ''', '"'
----------------------------------------------------------------------
    )                        end of \1
----------------------------------------------------------------------
    .+?                      any character except \n (1 or more times
                             (matching the least amount possible))
----------------------------------------------------------------------
    (?<!                     look behind to see if there is not:
----------------------------------------------------------------------
      \)                       ')'
----------------------------------------------------------------------
      (                        group and capture to \2:
----------------------------------------------------------------------
        ['"]                     any character of: ''', '"'
----------------------------------------------------------------------
      )                        end of \2
----------------------------------------------------------------------
    )                        end of look-behind
----------------------------------------------------------------------
  )                        end of look-behind
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------