prefixed(str) {
    let rule = this.virtual(str)
    if (this.disabled(rule.first)) {
      return rule.nodes
    }

    let result = { warn: () => null }

    let prefixer = this.prefixer().add[rule.first.prop]
    prefixer && prefixer.process && prefixer.process(rule.first, result)

    for (let decl of rule.nodes) {
      for (let value of this.prefixer().values('add', rule.first.prop)) {
        value.process(decl)
      }
      Value.save(this.all, decl)
    }

    return rule.nodes
  }
Return array of Declaration with all necessary prefixes