be on the books idiom
在（公司、组织、社团、运动队等的）名册上;受雇;属于
to be employed by a company, or (pay to) belong to a organization, society, sports team, etc.
There are 256 people on the books at the cement works. 水泥厂的在册员工有256人。
The nursery has 30 babies on the books and 13 on the waiting list. 托儿所的名册上有30个婴儿，等候入托的名单上还有13个。
US（尤指作为法律）正式记录
to be officially recorded, especially as a law
A ban on texting while driving is on the books in most states. 在大多数州，开车时发送手机短信是明文禁止的。