exaclty once; it will be replaced with the description calculated
according to the other rules. (``_desc`` substitution happens
after ``_colour`` substitution.)
+
+ * ``occulted`` [table, contents depend on ``occulted.method``]. If
+ specified, these pieces be occulted. For example, when a player
+ has them in their hand and the hand is active and owned by them,
+ only the occulted view (eg, the back of a playing card) will be
+ shown. This a table whose other contents depend on its key
+ ``method``, which must be a string:
+
+ * ``"ByColour"``: Occult by displaying a particular recolouring of
+ this piece. The sub-key ``colour`` names a recolouring - one of
+ the keys of the ``colours`` group parameter. When the piece is
+ occulted it will show that colour, instead of its actual colour.
+ In the description, ``_colour`` will be elided rather than
+ substitued (along with up to one of any spaces either side of it).
+
+ * ``"ByBack"``: Occult by displaying the back of this piece, as
+ specified by the ``back`` group parameter. The ``occulted`` table
+ must also contain a sub-entry ``ilk``, a string. Pieces which
+ have the same ``ilk`` display identically when occulted, even if
+ the different piece definitions imply different backs. (Whichever
+ pieces are first loaded define what the backs of a particular ilk
+ look.)
+
+ For pieces that are like cards, the ilk should be different for
+ cards which have different backs in the game. Generally, standard
+ playing cards should all specify ``card-back``.