Going inside (8)
I believe the answer is:
entering
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">going 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 entering that I've seen before include "Going inside" , "Going/coming in" , "Starting" , "Coming in" .)