Newspaper supplement (6)
I believe the answer is:
insert
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">newspaper supplement</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 insert that I've seen before include "Put between or within other things" , "Put thing in between others" , "Place within, pages of a publication say" , "Place in between other things" , "Push into" .)