Returns the sum of the specified numerical parameter/value combination among the sibling configurations.
double SiblingsParameterSum(string name; [bool includeSelf]; [string productTitle])
| name | The name of a parameter. | 
| includeSelf | Optional argument to include current configuration in the parameter sum. Default is false. | 
| productTitle | Optional filter to only include configurations of the specified product. | 
Example
SiblingsParameterSum("Length"; true)
Returns sum of the double or integer attribute "Length" from all sibling configurations including current configuration.
