+/* Given a 'path' (relative to the database path) return the document
+ * ID of the directory document corresponding to the parent directory
+ * of 'path' in 'parent_id'.
+ *
+ * The original 'path' can represent either a regular file or a
+ * directory, (in either case, the document ID of the parent will be
+ * returned). Trailing slashes on 'path' will be ignored, and any
+ * cases of multiple '/' characters appearing in series will be
+ * treated as a single '/'.
+ *
+ * If no directory document exists in the database for the parent, (or
+ * for any of its parents up to the top-level database path), then
+ * directory documents will be created for these (each with an mtime
+ * of 0).
+ *
+ * Return value:
+ *
+ * NOTMUCH_STATUS_SUCCESS: Valid value available in parent_id.
+ *
+ * NOTMUCH_STATUS_XAPIAN_EXCEPTION: A Xapian exception
+ * occurred and parent_id will be set to (unsigned) -1.
+ */