...
Split changes from an ACME subtree for merging with an external repo
NOTE: If you have to edit code that is in a subtree, commit those separately from other changes.
This workflow is to be used any time changes to an ACME subtree should be shared with the source external repository. For example, consider a bug fix made in the ACME MCT code. This workflow would allow contributing that fix upstream to MCT. Note that this workflow should not be used for the case where the ACME subdirectory was not brought into ACME as a subtree. That workflow is beyond the scope of this document.
...