This data structure describes an item in a PtTree.
The members include at least:
gen
A structure that describes a generic-tree item.
This structure includes state information for the item (whether or not
it's selected, the current item, damaged, out of view, expandable,
expanded, and so on),
its size, and links to other generic-tree items.
For more information, see
PtGenTreeItem_t.
set_img
The index into the tree's
Pt_ARG_TREE_IMAGES
resource of the image that's displayed when the item is set.
An item is considered set if its flags masked with the tree's
Pt_ARG_TREE_IMGMASK
resource give a nonzero value.
unset_img
The index of the image displayed when the item isn't set.
data
A pointer to arbitrary user data. This isn't used by the widget.
string
The string to be displayed for the item. This field is allocated the
appropriate amount of space when it's set.