Cannot find documentation for @key directive

Was trying to locate the documentation for the `@key` directive - Gen 1 / v5. But could not locate it.

Has it been removed? I only see the `@primaryKey` and `@index` directives in v6... Where can I find the `@key` directive documentation?

The issue names the @key directive and compares Amplify Gen 1/v5 with v6, but identifies no documentation file, test, or entry point. Start by searching the documentation repository for @key, @primaryKey, and @index, then verify whether the Gen 1/v5 directive reference exists and determine what documentation change would answer the question.

Written by the indexing model from the issue text.