These links were introduced in Moodle 1.6 to make it easier to TAB and key over side-blocks with many links. The text of the link is always hidden off-screen, which is acceptable for screen reader users, but not other keyboard-only users - bad accessibility.
- it initially hides the whole link off screen, then uses CSS pseudo-class :focus (" :active " - hack for IE 6) to put the link back in normal flow on keyboard TAB (position:static), making it visible. This moves the blocks below down, which I hope is acceptable for Dyslexics - the link stays hidden with no content movements for mouse users.
(I identified this problem and solution following workshops/ presentations at Techshare - thanks Bim Egan/ RNIB, and Hans Hillen/ Steve Faulkner/ The Paciello Group