Need to add a WPF Expander to the form. It works just fine other than when you drop down the expander the text does not wrap around (meaning it just continues in a straight line even if the expander height is set to 200 or more)

My expander code is this:
Dim tmpExpander As New Expander

tmpExpander.Header = Mid(theHeader, 1, 75) & "..."
Canvas.SetTop(tmpExpander, 24 * calRowNum)
Canvas.SetLeft(tmpExpander, 0)
tmpExpander.Width = 308
tmpExpander.Name = "exp_" & calTheRowNum & "_" & calRowNum
tmpExpander.Background = New SolidColorBrush(Colors.Transparent)
tmpExpander.IsExpanded = False
tmpExpander.Content = theHeader

Grid.SetRow(tmpExpander, 0)
Grid.SetColumn(tmpExpander, 0)

AddHandler tmpExpander.GotFocus, AddressOf expanderFocus
AddHandler tmpExpander.LostFocus, AddressOf expanderLostFocus
AddHandler tmpExpander.Collapsed, AddressOf expanderLostFocus
How can i add a textbox inside the above expander in order to use it's wrap-ability?