code: function check(node) {
      var url = node.url
      var reason
  
      if (identifiers.indexOf(url.toLowerCase()) !== -1) {
        reason =
          'Did you mean to use `[' +
          url +
          ']` instead of ' +
          '`(' +
          url +
          ')`, a reference?'
  
        file.message(reason, node)
      }
    }
docs: Check `node`.