Function is_env_name 

fn is_env_name(value: &str) -> bool

Does this string literal look like an environment variable’s name?

Shouty snake case, and ATUNE_PARAM_ — a prefix — is deliberately allowed to end with its separator. Restricting the shape is what keeps the scan from treating every string constant in the workspace as a variable; nothing else in the tree is spelled this way (measured: 12 matches, all of them real).