Function has_event_handler 

fn has_event_handler(lower: &str) -> bool

true if the text holds an inline on…=" event-handler attribute (a space or tab/newline, then on, then letters, then =). No benign SVG attribute begins with on, so the heuristic has no real false positives. Namespace declarations (xmlns) and href/src values are untouched. Coarse by design — see validate_svg for why that is sufficient in the <img> render context.