New pager, darling - that's sweet (5,5)

I believe the answer is:

grape sugar

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'sweet' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'new pager darling' is the wordplay.
'new' is an anagram indicator.
'darling' becomes 'sugar' (I've seen this in another clue).
'pager' anagrammed gives 'grape'.
'grape'+'sugar'='GRAPE SUGAR'

'that's' acts as a link.

Can you help me to learn more?

I've seen this clue in The Daily Express.

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