Re: [PATCH] git-sparse-checkout: clarify interactions with submodules

> +If your repository contains one or more submodules, then submodules
> +are populated based on interactions with the `git submodule` command.
> +Specifically, `git submodule init -- <path>` will ensure the submodule
> +at `<path>` is present, while `git submodule deinit [-f] -- <path>`
> +will remove the files for the submodule at `<path>` (including any
> +untracked files, uncommitted changes, and unpushed history).  Similar
> +to how sparse-checkout removes files from the working tree but still
> +leaves entries in the index, deinitialized submodules are removed from
> +the working directory but still have an entry in the index.
> +
> +Since submodules may have unpushed changes or untracked files,
> +removing them could result in data loss.  Thus, changing sparse
> +inclusion/exclusion rules will not cause an already checked out
> +submodule to be removed from the working copy.  Said another way, just
> +as `checkout` will not cause submodules to be automatically removed or
> +initialized even when switching between branches that remove or add
> +submodules, using `sparse-checkout` to reduce or expand the scope of
> +"interesting" files will not cause submodules to be automatically
> +deinitialized or initialized either.
> +
> +Further, the above facts mean that there are multiple reasons that
> +"tracked" files might not be present in the working copy: sparsity
> +pattern application from sparse-checkout, and submodule initialization
> +state.  Thus, commands like `git grep` that work on tracked files in
> +the working copy may return results that are limited by either or both
> +of these restrictions.