Be careful when you search for (4,3)
I believe the answer is:
look out
'be careful' is the definition.
(I've seen this before)
'you search for' is the wordplay.
I cannot really understand how this works, but
'you' could be 'u' (commonly used in online communication) and 'u' is present in the answer.
'search' could be 'look' (synonyms) and 'look' is located in the answer.
The remaining letters 'ot' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'when' acts as a link.
Can you help me to learn more?
(Other definitions for look out that I've seen before include "Be on your guard!" , "Take care" , "as Wenceslas did" , "makes one be careful!" , "Be watchful" .)