In one of the basic android tutorials I came across the resource/config identifier "-b+" that is not explained. Source can be found here: https://developer.android.com/training/basics/supporting-devices/languages.html
There it is stated that to support different locales one can make use of the following format when it comes to naming resource folders:
<resource type>-b+<language code>[+<country code>]
A concrete example for the us locale including language code and country code would be:
<project_root>/res/values-b+en+US/
My question is what does the -b stand for and how does this relate to the differing format omitting the "-b+" convention and on top makes use of the letter "r" to discern language code and region?
<project_root>/res/values-en-rUS
which can be found here: https://developer.android.com/guide/topics/resources/providing-resources.html#table2
Best regards, Ben