Function build_invocation_str 

pub fn build_invocation_str(
    spec: impl Into<TeXString>,
    args: Vec<Option<Tokens>>,
) -> Result<Tokens>

String entry point for Invocation (Perl: Invocation($token,@args) with a string first argument). The string is tokenized via TokenizeInternal; if it yields a single token, this reduces to build_invocation on that token. Otherwise the tokens are treated as an “anonymous macro” containing parameter markers like #1, and the arguments are substituted in.