Demonstrations of three elements (3-3)
I believe the answer is:
sit-ins
'demonstrations' is the definition.
(I've seen this before)
'three elements' is the wordplay.
I cannot really see how this works, but
'elements' could be 'tins' (tin is a kind of element) and 'tins' is located in the answer.
The remaining letters 'si' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?
(Other definitions for sit-ins that I've seen before include "Obstructive protests" , "In these protests, demonstrators refuse to leave a building" , "Forms of civil disobedience in which demonstrators refuse to leave a building" .)