Version 4.2.1

• NEW NavigationListBox style #2335 @StefanoRivolta-Previero
• ComboBox template update to match latest Material Design spec. #2428 @Keboo
• Calendar control updated to match latest Material Design spec with lots of additional customization. #2356 and #2412 @StefanoRivolta-Previero
• NavigationRail updated to match latest Material Design spec. #2348 @StefanoRivolta-Previero
• Clock updated to match latest Material Design spec. #2338 @StefanoRivolta-Previero
• Disabled look up controls updated to match latest Material Design spec. #2425 @Anopob
• UI improvements to MaterialDesignTabRadioButton #2402 and #2400 @JorisCleVR
• DrawerHost now supports CornerRadius #2333 @StefanoRivolta-Previero
• TreeView now supports ShowSelection and ExpanderSize attached properties. #2359 @StefanoRivolta-Previero
• Automatic color adjustment settings can be adjusted in the Color Tool in the demo app #2392 @FantasyTeddy
• PackIcon changes
• Full list of changes here

Please note the full list of breaking changes in 4.0.0 #1705

A big thank you to everyone who contributed (either logging issues or submitting PRs):
@Anopob
@bebenins
@Cohote
@drepamig
@FantasyTeddy
@HigherSY
@icameron
@icarousfff
@jdbriaris
@Job-madi
@JorisCleVR
@malu222
@rrs
@StefanoRivolta-Previero
@yosefmah