What one might read about in History Today sometimes (3,3,4)
I believe the answer is:
now and then
'sometimes' is the definition.
(I've seen this before)
'what one might read about in history today' is the wordplay.
I cannot quite see how this works, but
'one' could be 'the' (both can introduce a definite example of something) and 'the' is located in the answer.
'about' could be 'a' (abbreviation in Chambers) and 'a' is found in the answer.
'today' could be 'now' (synonyms) and 'now' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for now and then that I've seen before include "Occasionally" , "making a historical contrast" , "At times" , "Sometimes" .)