MarkupFilter filter = new EchoMarkupFilter();
PrintWriter writer = newPrintWriter();
IMarkupWriter mw = new MarkupWriterImpl("text/html", writer, filter);
mw.begin("span");
mw.attribute("width", "100%");
// Braces added by EchoMarkupFilter, to prove its there.
assertOutput("<span width=\"{100%}\"");