There is no code as such.
I have tried :
None error but none display an icon. The Doc above is for both DocumentContent and DockableContent.
Even in xaml I find the same thing with one exception. In the demo example you supply I see some docable tabs with icons. Trying to replicate this results in the following:
DocumentContent will not display an icon at all. DockableContent will only display an icon provided the dockable is hosted by a dockpane. This means that an independent window written to be added at runtime will not display a icon at all. With standard xaml
tabs I can add an icon(in xaml or c# a runtime) within a stack for the tabheader as it accepts an object, however looking at the code for the title in avalondock it only accepts a string.
I did a search on the web and found a comment from someone that they had to "tweek" the code to display icons, but they did not indicate what thy did.
I am in te process of upgrading an app from winforms using weifenlou docking which displays the icons I therefore need to replicate at least the original functionality.
just in case you might wonder, I can display icons using the same icon generation for display in menuitems - so this indicates that a valid icon object is being created.