The number of middle supports used in the stair. 
   Namespace:   Autodesk.Revit.DB.Architecture  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2013 
Syntax
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Field Value
0 if the stairs type has no middle support.Exceptions
| Exception | Condition | 
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| Autodesk.Revit.Exceptions ArgumentOutOfRangeException | When setting this property: The given value for supportsNumber is negative. | 
| Autodesk.Revit.Exceptions InvalidOperationException | When setting this property: The stairs type has no middle support so the data being set is not applicable. |