Let it remain as typescript's first laid out (4)
I believe the answer is:
stet
'let it remain' is the definition.
(I've seen this before)
'typescript's first laid out' is the wordplay.
'typescript's first' becomes 't' (sst letter of 'typescript').
'laid' becomes 'set' (synonyms).
'out' means one lot of letters goes inside another.
't' placed within 'set' is 'STET'.
'as' is the link.
(Other definitions for stet that I've seen before include "Instruction to printer" , "Instruction to leave spelling as is" , "Printing term" , "This must not be changed" , "(On proofs) instruction to cancel a correction" .)