in src/util/xml-helpers.js [217:228]
function graftXMLAttrs (doc, nodes, selector, xml, { overwrite = false } = {}) {
const target = module.exports.resolveParent(doc, selector);
if (!target) return false;
// saves the attributes of the original xml before making changes
xml.oldAttrib = Object.assign({}, target.attrib);
if (overwrite) target.attrib = {};
Object.assign(target.attrib, ...nodes.map(n => n.attrib));
return true;
}