`.documentXInclude` does nothing

[bruxisma]

Due to either the dependent libxml2 version being a bit outdated with current, or some other extent behavior, XXMLNode.Options.documentXInclude results in neither an error, nor a transformation of XML content.

import Foundation

#if canImport(FoundationXML)
  import FoundationXML
#endif

let mainXML = """
  <?xml version="1.0" encoding="utf-8"?>
  <root xmlns:xi="http://www.w3.org/2001/XInclude">
    <xi:include href="example.xml">
      <xi:fallback>
        <xi:include href="fallback.xml">
          <xi:fallback><error message="UH OH" /></xi:fallback>
        </xi:include>
      </xi:fallback>
    </xi:include>
  </root>
  """.data(using: .utf8)!

do {
  let doc = try XMLDocument(
    data: mainXML, options: [.documentTidyXML, .nodePreserveAll, .documentXInclude])
  print(doc)
} catch {
  print("Error parsing XML: \(error)")
}

The provided code sample should, at the very least, result in the xi:include element being replaced with at least the outer xi:fallback. Alternatively, an error should occur. Instead this fails silently and no transformations take place.