Long dashes in eastern manuscript (3)
I believe the answer is:
ems
'long dashes' is the definition.
(I've seen this in another clue)
'eastern manuscript' is the wordplay.
'eastern' becomes 'e'.
'manuscript' becomes 'ms' (abbreviation for manuscript).
'e'+'ms'='EMS'
'in' is the link.
(Other definitions for ems that I've seen before include "Measurement units in printing" , "Printers' measures" , "German town" , "Units used in printing" , "Units of print measure" .)