Crossword Genius

No-one at heart very nervous (3,2,4)

Ross

I believe the answer is:

all on edge

I'm a little stuck... Click here to teach me more about this clue!

'very nervous' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for all on edge that I've seen before include "Extremely nervous" , "Twitchy" .)

I've seen this clue in The Globe and Mail.
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