Function procedure_api_version 

pub fn procedure_api_version(procedure: &Procedure) -> Option<&str>

The @api_version("...") value a procedure declares, if any.

The parser (validate_procedure_api_version_attribute) guarantees at most one such attribute, a non-empty quoted string of ASCII alphanumerics, ., - and _, so the value is safe to splice into a URL path segment and into a double- or single-quoted string literal.