Selected is defined at the vtkMRMLNode leve, the fiducials can be selected by clicking on them in the Annotation GUI (clicking toggles selected, and there is a select all button). It needs another usability pass though.

I guess selected is the wrong word. the functionality in slicer3 is that some fiducials can be "selected" (made active) with the checkbox at the far left, and this is used as an inclusion/exclusion criteria (ie only seed or run a segmentation on "selected" fiducials).

If I understand correctly, "selected" in Slicer4 currently means the last node that was clicked on in the tree. The problem is, a user may need to click on some other nodes in the tree to make changes, and this will change the currently-selected nodes. Or, a user may need to have different sets of selected/unselected in different hierarchy nodes.

I think it is useful to have another, more permanent (checkbox-style) criteria that means "active" or "enabled" in addition to the current behavior.

Maybe there is a better paradigm, but I think the selected behavior was a very helpful addition to Slicer3... Thanks.

You're right, I was confused by the fact that Qt trees have selected rows/items and I thought that was linked to the Selected parameter on the nodes.
svn revision 17017 should fix this (still need some UI tweaks though, can only select all, but selecting/unselecting hierarchy nodes will propagate down):
http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=17017

Daniel added an unselect all button:
http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=17020