+/*
+ * Information used (along with the information in ref_entry) to
+ * describe a level in the hierarchy of references. This data
+ * structure only occurs embedded in a union in struct ref_entry, and
+ * only when (ref_entry.flag & REF_DIR) is set. In that case,
+ * (ref_entry.flag & REF_INCOMPLETE) determines whether the references
+ * in the directory have already been read:
+ *
+ * (ref_entry.flag & REF_INCOMPLETE) unset -- a directory of loose
+ * or packed references, already read.
+ *
+ * (ref_entry.flag & REF_INCOMPLETE) set -- a directory of loose
+ * references that hasn't been read yet (nor has any of its
+ * subdirectories).
+ *
+ * Entries within a directory are stored within a growable array of
+ * pointers to ref_entries (entries, nr, alloc). Entries 0 <= i <
+ * sorted are sorted by their component name in strcmp() order and the
+ * remaining entries are unsorted.
+ *
+ * Loose references are read lazily, one directory at a time. When a
+ * directory of loose references is read, then all of the references
+ * in that directory are stored, and REF_INCOMPLETE stubs are created
+ * for any subdirectories, but the subdirectories themselves are not
+ * read. The reading is triggered by get_ref_dir().
+ */