How do I create a custom contentpane header? I naively tried:
<ContentPane ...>
<ContentPane.Header>
<TextBox .... />
</ContentPane.Header>
</ContentPane>
But it doesn't work.
It depends on what you mean by a custom header. If you want to alter the caption area itself then you would want to retemplate/style the PaneHeaderPresenter. If you just want to alter the area within the PaneHeaderPresenter that is used to display the header of the ContentPane then you can provide a custom HeaderTemplate.