Adds or sets a RhinoScript user data item to the current document.
Rhino.SetDocumentData (strSection, strEntry, strValue)
| strSection | Required. String. The section name. | 
| strEntry | Required. String. The entry name. | 
| strValue | Required. String. The string value. | 
| String | The previous value if successful. | 
| Null | If no previous value exits, if not successful, or on error. | 
Rhino.SetDocumentData "MySection1", "MyEntry1", "MyValue1"
Rhino.SetDocumentData "MySection1", "MyEntry2", "MyValue2"
Rhino.SetDocumentData "MySection2", "MyEntry1", "MyValue1"