+# The function takes at most 2 arguments. The first argument is the
+# URL that navigates to the submodule origin repo. When relative, this URL
+# is relative to the superproject origin URL repo. The second up_path
+# argument, if specified, is the relative path that navigates
+# from the submodule working tree to the superproject working tree.
+#
+# The output of the function is the origin URL of the submodule.
+#
+# The output will either be an absolute URL or filesystem path (if the
+# superproject origin URL is an absolute URL or filesystem path,
+# respectively) or a relative file system path (if the superproject
+# origin URL is a relative file system path).
+#
+# When the output is a relative file system path, the path is either
+# relative to the submodule working tree, if up_path is specified, or to
+# the superproject working tree otherwise.