Returns the URI as an absolute Uri?: Uri itself when it is absolute, else resolved against the document's UriBase. Nothing is fetched.
public Uri? ResolveUri()
null when there is no URI, or it is relative and the document has no base URI, or it is not a URI at all.ISO 32000-2 §12.6.4.8, Tables 210 and 211 (RFC 3986 reference resolution). The result is untrusted data from the document.