Change record status: 
Project: 
Introduced in branch: 
8.8.x
Introduced in version: 
8.8.0-alpha1
Description: 

Themes can now be marked experimental by adding the following to their *.info.yml file:

experimental: true

This results in similar installation warnings as for modules that are in the Core (Experimental) package.

Impacts: 
Themers
Updates Done (doc team, etc.)
Online documentation: 
Not done
Theming guide: 
Not done
Module developer documentation: 
Not done
Examples project: 
Not done
Coder Review: 
Not done
Coder Upgrade: 
Not done
Other: 
Other updates done