in src/ConfigChanges/munge-util.js [120:127]
function getElements ({ files }, [fileName, selector], opts = { create: false }) {
if (!files[fileName] && !opts.create) return [];
const { parents: fileChanges } = (files[fileName] = files[fileName] || { parents: {} });
if (!fileChanges[selector] && !opts.create) return [];
return (fileChanges[selector] = fileChanges[selector] || []);
}