This is very confusing as seen in #12974 or #12906. My suggestion would be "legacy."
var outName = getTempFile("~preprocess", ".css");
  builder.preprocessCSS(mode, source, outName);
  var out = fs.readFileSync(outName).toString();
  fs.unlinkSync(outName);
  if (cleanup) {
    
    var reg = /\n\/\* Copyright(.|\n)*?Mozilla Foundation(.|\n)*?\*\//g;
    out = out.replace(reg, "");
  }
  var i = source.lastIndexOf("/");
  return createStringSource(source.substr(i + 1), out);
}
function preprocessHTML(source, defines) {