updated for version 7.3.627 Problem: When using the "n" flag with the ":s" command a \= substitution will not be evaluated. Solution: Do perform the evaluation, so that a function can be invoked at every matching position without changing the text. (Christian Brabandt)

Results:
tab page 2
this is tab page 3
this is tab page 1
this is tab page 4
gettabvar: pass
settabvar: pass
tab drop 1: pass
tab drop 2: pass
tab drop 3: pass
1
6
4
8
10
1
10
4
6
E474 caught.