Change record status: 
Project: 
Introduced in branch: 
8.2.x
Introduced in version: 
8.2.0
Description: 

The BlockRegion migration process plugin formerly expected its input value to be an array of three strings: [$source_region, $source_theme, and $destination_theme], in that order. As of #2753939: BlockRegion process plugin should be source theme-aware, the order of the inputs has changed; it now expects an input array of [$source_theme, $destination_theme, $source_region]. This change was introduced in order to make static mapping of the destination region more intuitive to developers.

Impacts: 
Module developers