Adding a markup filter
In some very rare cases it might be necessary to add an additional markup filter to the default list. Lets say you want to log a warning or throw an exception in case of an empty src attribute like <img src="">. The Image component is not able to handle it because the wicket id is missing. A markup filter in contrast iterates over all xml tags and is able to detect the problem and to throw an exception.
Note: a markup filter is not able to detect an AttributeModifier changing the src attribute to an empty string.
Wicket 1.4:
It's maybe a good idea to allow your MarkupParserFactory accept a list of filters which might get appended on creation of the parser in 'newMarkupParser'.