ier for
  the transaction will be in ``HG_TXNID``. The rest of the available data will
  vary according the transaction type. New changesets will add ``$HG_NODE``
  (the ID of the first added changeset), ``$HG_NODE_LAST`` (the ID of the last
  added changeset), ``$HG_URL`` and ``$HG_SOURCE`` variables.  Bookmark and
  phase changes will set ``HG_BOOKMARK_MOVED`` and ``HG_PHASES_MOVED`` to ``1``
  respectively, etc.