public boolean resolve(final MarkupContainer container, final MarkupStream markupStream,
final ComponentTag tag)
{
if (tag instanceof WicketTag)
{
WicketTag wtag = (WicketTag)tag;
if (wtag.isMessageTag())
{
String messageKey = wtag.getAttributes().getString("key");
if ((messageKey == null) || (messageKey.trim().length() == 0))
{
throw new MarkupException(
"Wrong format of <wicket:message key='xxx'>: attribute 'key' is missing");
}