Place inside (6)
I believe the answer is:
insert
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">place inside</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 insert that I've seen before include "Add in" , "Push into" , "Loose sheet within magazine" , "Put in; enclosure" , "Put thing in between others" .)