Returns whether the text represents a root-relative link. These look like
/this and are resolved relative to a base URL’s origin. This can also be called
“domain-relative URL” (by MDN) and “path-absolute-URL string” (by WHATWG).
From MDN:
Attempts to parse a string which might represent a URL or a filesystem path.
Returns Ok if it is unambiguously a valid URL, otherwise returns Err
with the original input.