Range of former shelter (6)
I believe the answer is:
'range' is the definition.
(I've seen this in another clue)
'former shelter' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'shelter' becomes 'tent' (canvas shelter).
'of' acts as a link.
(Other definitions for extent that I've seen before include "Measure" , "Compass, scope" , "stretch" , "Area something covers" , "Range or scope of something" .)