Function find_fn_doc 

pub fn find_fn_doc(
    module: Option<&str>,
    fn_name: &str,
) -> Option<(&'static StdEntry, &'static FnEntry)>

Searches all stdlib entries for a function whose signature starts with fn_name(.

module narrows the search to a specific stdlib module (e.g. "io", "math"). Accepts both bare names (print) and qualified names (std::io::print).

Returns None if no match is found.