This page is for anyone modifying code that is part of an external which was brought in via a git submodule. Git submodules used for larger external projects where ACME development is expected to take place in the external repository, such as MPAS. For other applications, see git subtree.
Before delving into the details of the workflow, we'll explain a bit about what submodules are and some of their benefits. A submodule is in essence a nested git repository within another git repository. The parent repository stores a file which tells git that it has a child repository, what it's clone URL is, what commit the parent wants from within that repository, and where the repository should be clone to (i.e. the local path within the parent repository). For example, if the external was MPAS-O the information the parent might store is:
...