Mixing Toggle Selection and Object Selection in the same interface can lead to a confusing interface. Referring back to Yahoo! Bookmarks, you'll see an odd situation arise during drag and drop (Figure 3-14).
Figure 3-14. In Yahoo! Bookmarks, one item is selected, but two items can be dragged by dragging on the unselected item
There are a few important issues to consider when using Hybrid Selection.
In the left panel of Figure 3-14, one bookmark element is selected (notice the checkbox Toggle Selection). The second bookmark element ("Dr. Dobb's") is unselected (the checkbox is clear). In the right panel of Figure 3-14, clicking and dragging on the unselected bookmark element initiates a drag. The drag includes both the selected element and the unselected element. Since only one is shown as selected, this creates a confusing situation.
This occurs because three things are happening in the same space:
Toggle Selection is used for selecting bookmarks for editing, deleting, etc.
Object Selection is used for initiating a drag drop.
Mouse click is used to open the bookmark on a separate page.
The problem is that more than one interaction idiom is applied to the same place on the same page. In this case, if you happen to try to drag, but instead click, ...