Massenet opera; it has been adapted (5)

I believe the answer is:

thais

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

'massenet opera' is the definition.
(I've seen this in another clue)

'it has been adapted' is the wordplay.
'it has' anagrams to 'THAIS'.
But, I'm not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for thais that I've seen before include "Asians" , "Natives of former Siam" , "orientals" , "Siamese people" , "Opera" .)

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

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