function createElementNS(name, namespaceURI) {
        return !namespaceURI || namespaceURI === NS_XHTML ?
            doc.createElement(name) :
            doc.createElementNS(namespaceURI, name);
    }
Create an element, optionally with a known namespace URI.

@param {string} name the element name, e.g. 'div' or 'svg'
@param {string} [namespaceURI] the element's namespace URI, i.e. the value of
its `xmlns` attribute or its inferred namespace.

@return {Element}