code: function isKnown(ruleId, verb, pos) {
        var result = known ? known.indexOf(ruleId) !== -1 : true
  
        if (!result) {
          file.warn('Unknown rule: cannot ' + verb + " `'" + ruleId + "'`", pos)
        }
  
        return result
      }
docs: /* Helper to check (and possibly warn) if a ruleId is unknown.