Error message? (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">error message?</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 oops that I've seen before include "Exclamation on making obvious mistake" , "Exclamation on making a minor mistake" , "Exclamation on making minor error" , "I've slipped" , "Oh dear, that was careless!" .)