Get all the custom Panels on Add-Ins tab of Revit. 
   Namespace:   Autodesk.Revit.UI  
  Assembly:   RevitAPIUI  (in RevitAPIUI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
Syntax
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| Visual Basic | 
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| Visual C++ | 
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Remarks
 The built-in panels won't be included and the panels added to tabs other than Add-Ins will not be included. This method is not supported in Macros.