Insertion mark (5)
I believe the answer is:
caret
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">insertion mark</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for caret that I've seen before include "Sign something's lacking" , "Proofreader's sign of omission" , "Proofreading sign for 'Insert'" , "A sign something is missing" , "Indicator of omission" .)