a. 规定的, 指定的, 规范的

[法] 规定的, 指示的, 命令

[ adj ]
pertaining to giving directives or rules
<adj.all>
prescriptive grammar is concerned with norms of or rules for correct usage

Prescriptive \Pre*scrip"tive\, a. [L. praescriptivus of a
demurrer or legal exception.]
1. (Law) Consisting in, or acquired by, immemorial or
long-continued use and enjoyment; as, a prescriptive right
of title; pleading the continuance and authority of long
custom.

The right to be drowsy in protracted toil has become
prescriptive. --J. M. Mason.

2. Of or pertaining to the doctrine that acceptable
grammatical rules should be prescribed by authority,
rather than be determined by common usage.
[PJC]