Section 12.2.3 states that

"A composable function can be invoked with additional path segments or system query options appended to the path that identifies the composable function as appropriate for the type returned by the composable function."

Unfortunately it doesn't state which path segments and system query options can be used even if the function is not composable.

The rules for the path segments /$value and /$count in Part 2, sections 4.7 and 4.8, and for system query options in Part 2, section 5.1, only take the response type into account, so these should also apply to non-composable functions.