Sounds english and it is lol
there are many stories for the origin but no definitive one. a common explanation is that they stands for (P)Pleases and Thank yous(Q). But that particular expression came into common use AFTER "P's and Q's".
they can also stand for prime and quality but the expression does not make sense grammatically.
Answer: alliteration and rhyme
Alliteration is the repetition of identical initial consonant sounds in closely associated syllables or words. In this line, the author uses alliteration when he uses the words "silken sad."
A rhyme is a repetition of similar sounds in the final syllables of two words. Rhymes are most often find in poetic writing. In this case, the author's use of the words "uncertain" and "curtain" are examples of rhymes.
Could u be more elaborate on the question
C have a good day so a or c