I think that one of the things that's confusing here is that some of these new variable names begin with a _ character. Even though there has never been any prohibition against beginning an environment variable name with a _, we, or at least I tend to automatically assume that any variable beginning with _ is a TCC system variable. I had to read the help several times before it registered that these were ENVIRONMENT variables.Because they're variables generated by a variable function, not a command. The variable parsing nesting would get ugly.
Why do you care?