Function is_binding_extension 

pub fn is_binding_extension(ext: &str) -> bool

true when at least one registered binding declares ext as its extension. Used by \input’s heuristic to decide whether \input{name.<ext>} should consult the binding registry — e.g. .sty, .cls, .def, .pool, code.tex are all valid binding extensions, while .eps, .png, .bib are not. Matches by extension only (the name is checked separately by dispatch()’s exact lookup).