[#8BFBF955FAB8E0E9E52DBB8A810D8ABE05A066AA]
Return true if a userinfo is present
bool has_userinfo() const noexcept;
This function returns true if this contains a userinfo.
assert( url_view( "http://jane%2Ddoe:pass@example.com" ).has_userinfo() );
Constant.
Throws nothing.
userinfo = user [ ":" [ password ] ]
authority = [ userinfo "@" ] host [ ":" port ]