Thing inserted (5)
I believe the answer is:
inset
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">thing inserted</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for inset that I've seen before include "Smaller map" , "Implant" , "Not taking proper care" , "Extra page or piece added to enlarge" , "subsidiary diagram" .)