code: function seq(...items) {
      const flatDef = _.flatMap(items, toDefinition)
      const definition = new Flat({ definition: flatDef })
  
      const orgTextParts = _.map(items, toOriginalText)
      definition.orgText = `seq(${orgTextParts.join(", ")})`
  
      return {
          toRule: toRule,
          definition: definition
      }
  }
docs: rule: A B C ...