RNG attribute completion doesn't generate the proper prefix if the namespace is not declared

[angelozerr]

Given this XML file bound to RelaxNG file:

<?xml version="1.0" encoding="utf-8"?>
<?xml-model href="http://docbook.org/xml/5.0/rng/docbook.rng" schematypens="http://relaxng.org/ns/structure/1.0"?>
<book xmlns="http://docbook.org/ns/docbook">
    <acknowledgements></acknowledgements>
</book>

When completion is triggered on <acknowledgements |> it show attributes, but it doesn't take care of prefix, if the namespace is not declared correctly. For instance it shows actuate although actuate should be linked to http://www.w3.org/1999/xlink namespace by using xlink prefix.

Please note that If you declare the xlink namespace

<book xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" >

The completion shows correctly completion item with xlink:actuate.

To fix this issue, it should be nice to get xlink prefix from the grammar, and when completion is applied, it should insert in the book element the proper namespace xmlns:xlink="http://www.w3.org/1999/xlink" like the follwoing demo: