-There are also some ancillary programs that can be viewed as useful
-aids for using the core commands but which are unlikely to be used by
-SCMs layered over git.
+Although git includes its
+own porcelain layer, its low-level commands are sufficient to support
+development of alternative porcelains. Developers of such porcelains
+might start by reading about gitlink:git-update-index[1] and
+gitlink:git-read-tree[1].
+
+We divide the low-level commands into commands that manipulate objects (in
+the repository, index, and working tree), commands that interrogate and
+compare objects, and commands that move objects and references between
+repositories.