OptionalpreviewIDS 1.1 PREVIEW (unstable). Without ids11, a document using a 1.1
candidate feature is refused with IDS11PreviewRequiredError; with it,
such a document is written against the 1.1 schema location. A document
using no 1.1 feature is written as IDS 1.0 either way, byte for byte.
What
writeIdsXmlmay write, as opposed to how (IdsXmlFormat).