own (optional) icon and a label. An item may be either collapsed (meaning that
its children are not visible) or expanded (meaning that its children are
shown). Each item in the tree is identified by its {\it itemId} which is of
-opaque data type {\it wxTreeItemId}.
+opaque data type {\it wxTreeItemId}. You can test whether an item is valid
+by calling wxTreeItemId::IsOk.
The items text and image may be retrieved and changed with
\helpref{GetItemText}{wxtreectrlgetitemtext}/\helpref{SetItemText}{wxtreectrlsetitemtext}
\helpref{IsSelected}{wxtreectrlisselected},
\helpref{IsVisible}{wxtreectrlisvisible}, \helpref{IsBold}{wxtreectrlisbold}
and \helpref{IsExpanded}{wxtreectrlisexpanded}. Only one item at a time may be
-selected, selecting anopther one (with
+selected, selecting another one (with
\helpref{SelectItem}{wxtreectrlselectitem}) automatically unselects the
previously selected one.
EVT\_TREE\_ITEM\_EXPANDING event is received: then all items lying immediately
under the item being expanded should be added, but, of course, only when this
event is received for the first time for this item - otherwise, the items would
-be added twice if the user expands/collapses/reexapnds the branch.
+be added twice if the user expands/collapses/re-expands the branch.
The tree control provides functions for enumerating its items. There are 3
groups of enumeration functions: for the children of a given item, for the
\helpref{GetNextChild}{wxtreectrlgetnextchild} should be the same variable (and
that nothing should be done with it by the user code).
-Among other functionalities of the tree control are: item sorting with
+Among other features of the tree control are: item sorting with
\helpref{SortChildren}{wxtreectrlsortchildren} which uses the user-defined comparison
function \helpref{OnCompareItems}{wxtreectrloncompareitems} (by default the
comparison is the alphabetic comparison of tree labels), hit testing
may be used to change the current selection. <HOME> and <END> are used to go to
the first/last sibling of the current item. '+', '-' and '*' expand, collapse
and toggle the current branch. Note, however, that <DEL> and <INS> keys do
-nothing by default, but it is custom to associate them with deleting item from
-a tree and inserting a new one in it.
+nothing by default, but it is usual to associate them with deleting item from
+a tree and inserting a new one into it.
+