Re: [libvirt] [PATCH 3/6] conf: tighten <domainsnapshot> schema

This patch is my first experience playing with nested grammars, as documented in http://relaxng.org/tutorial-20011203.html#IDA3PZR. I plan on doing more overrides in order to make the RelaxNG grammar mirror the C code refactoring into a common virStorageSource, but where different clients of that source do not support the same subset of functionality. By starting with something fairly easy to validate, I can make sure my later patches will be possible. One way to test this patch: s/qed/raw/ in the file tests/domainsnapshotxml2xmlin/disk_snapshot.xml, then run make -C tests check TESTS=domainsnapshotschematest. Pre-patch, the file will pass the schema, even though attempts to use that description with virDomainSnapshotCreateXML will fail because raw files cannot have a backing store. Post-patch, the file will fail virt-xml-validate. * docs/schemas/domainsnapshot.rng (domain): Use nested grammar to avoid restricting <domain>. (storageFormat): Override for tighter usage. * docs/schemas/storagecommon.rng (startupPolicy): Create a no-op default. * docs/schemas/domaincommon.rng (storageFormat): Cross-reference. (startupPolicy): Move the non-trivial define... * docs/schemas/domain.rng (startupPolicy): ...here.