code: function insert(match, commenttype, statement, file) {
      var location = path.resolve(reference, file)
        , data = '';
  
      //
      // If it's not an absolute path, try to require.resolve the file.
      //
      if (!fs.existsSync(location)) try {
        location = require.resolve(file);
      } catch (e) { }
  
      if (!fs.existsSync(location)) {
        return self.critical(
            '// [square] @%s statement %s in %s does not exist'
          , statement
          , file.red
          , reference.red
        );
      }
  
      if (~seen.indexOf(location)) {
        return self.critical('recursive [square] import statement detected %s', match);
      }
  
      // We processed the file, mark it as seen to protect us against recursive
      // includes.
      seen.push(location);
  
      data += self.commentWrap('[square] Directive: ' + location, extension);
      data += fs.readFileSync(location, 'utf8').trim();
  
      // Pass the contents back in to the directive again so we can also process
      // the directives inside the directive.
      return self.directive(data, extension, path.dirname(location), seen);
    }
docs: Process the directive.
  
  @param {String} match complete matched result
  @param {String} commenttype type of comment
  @param {String} statement import statement name
  @param {String} file the file that needs to be inlined
  @returns {String}
  @api private