Functions to manage namespace usage

[apb2006]

Prior to saving XML generated in XQuery I often tweak the namespace usage.
This makes the XML lighter and clearer for the casual reader and is sometimes mandated by users and systems.
I think providing builtin solutions for these cases would ease these tasks.

Common cases are:

1. Remove unused prefixes
   Example: the function presented at https://stackoverflow.com/questions/23002655/xquery-how-to-remove-unused-namespace-in-xml-node

2. Make a namespace the default wherever it is used.
   Example: functx:change-element-ns-deep($nodes,$targetns,"")
   See http://www.xqueryfunctions.com/xq/functx_change-element-ns-deep.html

3. Remove the use of all/some namespaces
   Example: BaseX https://docs.basex.org/wiki/Utility_Module#util:strip-namespaces

A somewhat related issue #266

[michaelhkay]

I would suggest a function rename-nodes($node, $map) that copies a subtree, renames the element (and perhaps attribute) nodes according to rules in the map, and then drops unused namespace nodes.

An example of a rule might be map{"Q{http://something/ns}*" : "Q{}*"} which renames all elements in namespace http://something/ns to be in no namespace. The basic idea is that rules can match either the namespace URI or the local name or both (with a precedence system similar to xsl:strip-space) and the target name can retain either the namespace URI or the local name or both or neither.

This is primarily about namespace URIs, not prefixes, on the assumption that prefixes don't actually matter.

[apb2006]

The goal of case 2 above is to replace use of a prefix with an explicit xmlns= where required.
Could this be done like map{"Q{http://docbook.org/ns/docbook}*" : ""}

let $book:=
<d:book xmlns:d="http://docbook.org/ns/docbook">
        <d:info>
             <title xmlns="http://docbook.org/ns/docbook">Another fine book</title>
        </d:info>
</d:book>

return rename-nodes($book, map{"Q{http://docbook.org/ns/docbook}*" : ""})

<book xmlns="http://docbook.org/ns/docbook">
  <info>
    <title>Another fine book</title>
  </info>
</book>

[cedporter]

rename-nodes() definitely sounds useful, but it would not take the place of strip-namespaces() described in the link in #3 in BaseX. That function, when passed an empty string, will remove all namespaces. With rename-nodes(), you'd have to explicitly specify all namespaces in the doc to produce the same behavior.

[ndw]

This is related to #266

[ndw]

The CG at the F2F meeting in Prague conclude that several users have asked for this, and it isn't straight-forward in XQuery, so we should do something to address it.