David T. Lewis uploaded a new version of System to project The Trunk:
http://source.squeak.org/trunk/System-dtl.1225.mcz

==================== Summary ====================

Name: System-dtl.1225
Author: dtl
Time: 11 April 2021, 9:50:52.898233 pm
UUID: a96e7afc-11cc-48c8-8e72-d63f6295e092
Ancestors: System-tonyg.1224

Symbol>>asMutator is used by Seaside, do not deprecate it. Instead let it be a synonym for the preferred Symbol>>asSimpleSetter.

=============== Diff against System-tonyg.1224 ===============

Item was added:
+ ----- Method: Symbol>>asMutator (in category '*System-Support') -----
+ asMutator
+ 	"Synonym for asSimpleSetter, retained for support of external packages such as Seaside"
+ 
+ 	^ self asSimpleSetter!