Function is_scheme_relative_link 

pub(crate) fn is_scheme_relative_link(text: &str) -> bool

Returns whether the text represents a scheme-relative link. These look like //example.com/subpath. From MDN:

Scheme-relative URL: //developer.mozilla.org/en-US/docs/Learn_web_development — only the protocol is missing. The browser will use the same protocol as the one used to load the document hosting that URL.