Typewriter key (3)
(Another definition for backspace that I've seen is " key used to find character already in?".)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">typewriter key</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tab that I've seen before include "Tally of orders in bar" , "Ring pull" , "Till bill" , "ticket" , "Flap; illicit drug pill (slang)" .)