Currently, all component tag attributes are escaped.With html5 data- attributes, much more values can be considered valid depending on the tag attribute and some should not be escaped.
For example, bootstrap tooltips use the "data-title" attribute to set the content of a tooltip. Using Wicket's tag attributes, it's not possible to set the value "<b>hello world</b>" as the data-title since it is escaped.
ComponentTag#writeOutput() is the method which calls Strings.escapeMarkup(value); and escapes tag values. This is called by Component#renderComponentTag().
There should be a way to disable component tag escaping either per-tag or per-component.