As Andrew wrote on the Linux-HA Mailinglist:
Or, if you simply must view it online, go to http://hg.clusterlabs.org/pacemaker/dev/file/tip/xml/crm-1.0.dtd which is always the latest.
(Andrew's original mail to the list can be found at http://lists.linux-ha.org/pipermail/linux-ha/2007-August/026854.html)