David T. Lewis uploaded a new version of Collections to project Squeak 4.6:
http://source.squeak.org/squeak46/Collections-topa.638.mcz

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

Name: Collections-topa.638
Author: topa
Time: 8 July 2015, 4:17:26.216 pm
UUID: aa218acf-c29b-4df1-ab0a-285f1f71c6a7
Ancestors: Collections-topa.637

Let's say PluggableTextAttributes are not serializable.

=============== Diff against Collections-topa.637 ===============

Item was added:
+ ----- Method: PluggableTextAttribute>>writeScanOn: (in category 'as yet unclassified') -----
+ writeScanOn: aStream
+ 	"Impossible for this kind of attribute"
+ 	^ self shouldNotImplement
+ 	!