Documentation for the "version" key's accepted values

[macintacos]

Describe the feature

I've been trying to understand what the full list of values are accepted by packer for the version key, but I can't seem to find any explanation for it. I only see examples in the README and docs specifying some semver value like "2.1.0", however it's not clear if it accepts other values like "~2.1"/"^2.1"/"<some_git_hash>"/"<some_branch_name>"/etc.

I'm trying to be more conscious about what versions I am allowing in my configuration, so having this documented would be very much appreciated. Thanks!