Function try_autoload 

pub fn try_autoload(token: &Token) -> bool

Ask the registered hook whether token should pull the LaTeX kernel in.

true ⇒ the kernel was loaded and token now has a meaning, so the caller must push it back and re-resolve. false ⇒ nothing happened; take the ordinary bounded Error:undefined path.

Cold path only — every caller is a site that was already about to raise an undefined-CS error. With no hook registered (a bare latexml_core embedding) this is an atomic load and a false.