Is `command -v` option required in a POSIX shell? Is posh compliant with POSIX?

Question

I am using posh to test my shell script that I want to run successfully on any POSIX compliant shell. While doing so, I found that the command -v option is not

Answer 1

See the [UP] margin code next to the definition of -v. Per the list of margin code notations (emphasis added):

^[UP] User Portability

The functionality described is optional.

Where applicable, utilities are marked with the UP margin legend in the SYNOPSIS section. Where additional semantics apply to a utility, the material is identified by use of the UP margin legend.

Thus, it's black-letter POSIX: This functionality is optional.