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Window identifiers 
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Identifiers do not need to be unique across the entire application just so long as
they are unique within a particular context, such as a frame and its children.

To avoid problems I will define ranges for dialogs that can be visible at the
same time. According wxWidgets documentation you can use wxID_HIGHEST to determine
the number above which it is safe to define your own identifiers. Or, you can
use identifiers below wxID_LOWEST.

Also, there is the posibility of using global function ::wxNewId(). This function
returns a unique Id (there is an internal global id counter and this function returns
wxID_HIGHEST and increments its value).


MainFrame: 1000 - 1299
StatusBar: 1300 - 1319

TextBookFrame: 2000-2099

Dialogs: 2100-2199

Tool box: 2200-2299

Html: Main Controls: 3000-3499
      Aux controls:
            ScoreCtrol: 35xx
            CountersAuxCtrol: 36xx
      Exercises:
        Base class:  3700-3719
        Specific classes: 3720-3799 
            
