code: function resolveId (prop) {
      if (rule[prop] === null || typeof rule[prop] === 'number') return
  
      // Resolve the property to an index
      var j = self._getRuleIndex(rule.id)
      if (j < 0)
        self._error( new Error('Atok#_resolveRules: ' + prop + '() value not found: ' + rule.id) )
        
      rule[prop] = i - j
    }
docs: Perform various checks on a continue type property