2.1.1 [WC3-LONGDESC] Section 3. The longdesc Attribute

V0001: No user interface provided

The specification states:

 3.0.3 User Agents
 If the longdesc value is valid, User agents must make the link available to all users 
 through the regular user interface(s).

All document modes (All versions)

There is no user interface provided to access the longdesc URL.