Function scheme_allowed 

pub fn scheme_allowed(url: &str) -> bool

Whether a [label](url) link may point at url under the default scheme list.

Anything else — javascript:, data:, file:, or an unrecognized scheme — makes the whole construct render as literal text, delimiters included, so the user sees exactly what was typed rather than a link they can’t inspect. A view with its own scheme list uses parse_inline_with.