Function percent_encode_fragment 

pub fn percent_encode_fragment(reference: &str) -> String

Percent-encodes the characters RFC 3986 forbids in a URI reference’s fragment.

Unlike url_encode, the fragment’s own syntax survives: the leading #, the / and ? separators, the sub-delimiters and any existing %XX escape all pass through. Use it for values that are URI references rather than opaque data, such as JSON Schema $refs.