file.marshall(th, self.desc or '')

  self.desc  = file.unmarshall_string(th)

function portal_desc(desc, props)
  return PortalDescriptor:new(desc, props)

function portal_desc(props)
  return PortalDescriptor:new(props)

           K. Portal vaults

K.   Portal Vaults
------------------
Portal vaults are vaults accessed by portals in the dungeon (bazaars
are a special case of portal vaults). You can create custom portal
vaults as follows:
Define a vault to hold the portal itself:
# Bare-bones portal vault entry
NAME: portal_generic_entry
TAGS: allow_dup
ORIENT: float
MARKER: O = lua:one_way_stair { desc = "A portal to places unknown", \
                                dst = "generic_portal" }
KFEAT: O = enter_portal_vault
MAP
O
ENDMAP
Portal entries must contain a portal vault entry (enter_portal_vault).
This feature must always have a marker that provides the portal with a
description ("A portal to places unknown") and a destination
("generic_portal").
This will produce a portal, but attempting to use it will trigger an
ASSERT since there's no map for the destination. So we create a
destination map like so:
NAME: portal_generic_generic
# Tag must match dst value of portal in entry.
TAGS: generic_portal allow_dup
ORIENT: encompass
MONS: ancient lich
KFEAT: > = exit_portal_vault
MAP
xxxxxxxxxxx
x111111111x
x1A111111>x
x111111111x
xxxxxxxxxxx
ENDMAP
Note that the entry point into the map will be a stone arch. You must
provide an exit to the dungeon explicitly (KFEAT: > =
exit_portal_vault) or the player will not be able to leave.
Stairs will not work right in portal vaults, do not use them.
You can use multiple maps with the destination tag (generic_portal),
and the dungeon builder will pick one at random.