ISSUE-233 (the # <empty> fragment id): Need clarification of why # is invalid as a link target [mobileOK Basic tests]

ISSUE-233 (the # <empty> fragment id): Need clarification of why # is invalid as a link target [mobileOK Basic tests]

http://www.w3.org/2005/MWI/BPWG/Group/track/issues/

Raised by: Jo Rabin
On product: mobileOK Basic tests

Another one on behalf of the Dom-on-high:

Why does the mobileOK basic test claim that 

 "If there is no target for the reference or it is invalid (e.g. '#'),
warn"

The answer being that a null string is not a valid IDREF but # always takes you to the top of the page anyway.

Does this merit an explanatory note?