function makeStructureNS(namespaceURIs, structure, structureNS) {
  structureNS = structureNS !== undefined ? structureNS : {};
  let i, ii;
  for (i = 0, ii = namespaceURIs.length; i < ii; ++i) {
    structureNS[namespaceURIs[i]] = structure;
  }
  return structureNS;
}
Create a namespaced structure, using the same values for each namespace.
This can be used as a starting point for versioned parsers, when only a few
values are version specific.
@param {Array<string>} namespaceURIs Namespace URIs.
@param {T} structure Structure.
@param {Object<string, T>} [structureNS] Namespaced structure to add to.
@return {Object<string, T>} Namespaced structure.
@template T