This production rules out a PI target of "XML", "xml", or anything in between. Of course this technically allows the use of something like <?XmlStyle?>, but that would be unwise.
It might even be illegal; in an outburst of sloppiness, the spec, in its definition of Name, says that names beginning with the letters x, m, l, are "reserved", whatever that means.
Anyhow, don't use 'em.
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