Publishing a 2.X and 3.X Compatible plugin

I see on this page Migrate Plugin from Piwik 2.X to Piwik 3: Develop - Piwik Analytics - Developer Docs - v3 it states “It is still possible to release updates for the branch that is compatible with Piwik 2.”. It doesn’t go into detail as to how this 2.X branch should be named or handled however. Any ideas? Examples?