ensureNamespace: Ensure that the node has a definition for particular XML namespaces
Description
This function is a helper function for use in creating XML content.
We often want to create a node that will be part of a larger XML tree
and use a particular namespace for that node name. Rather than
defining the namespace in each new node, we want to ensure that
it is define on an ancestor node. This function aids in that task.
We call the function with the ancestor node or top-level document
and have it check whether the namespace is already defined or have
it add it to the node and return.
This is intended for use with XMLInternalNode objects
which are direclty mutable (rather than changing a copy of the node
and having to insert that back into the larger tree.)
Usage
ensureNamespace(doc, what)
Arguments
doc
an XMLInternalDocument or XMLInternalNode on
which the namespace is to be defined. If this is a documentm, we use
the root node.
what
a named character vector giving the URIs for the namespace
definitions and the names giving the desired prefixes
Value
This is used for the potential side effects of modifying the
XML node to add (some of) the namespaces as needed.