Crossword Genius

No one has birth as complicated as he imagined! (5,8)

Ross

I believe the answer is:

heath robinson

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

'imagined' is the definition.
Both the definition and answer are adjectives.
Maybe there's an association between them I don't understand?

'no one has birth as complicated as he' is the wordplay.
'no one has birth' anagrams to 'HEATH ROBINSON'.
But, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for heath robinson that I've seen before include "Absurdly complicated in design (for a machine)" , "with unnecessary trimmings?" , "Cartoonist known for strange machines" , "Cartoonist noted for fantastic machinery" , "Ridiculously complicated in design" .)

I've seen this clue in The Guardian.
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