Conditional Group-based operators

These operators use a scope based on a group. They can work with sets or lists, retaining data type, or may use expressions evaluating as lists or sets.

The group may be any designator from:

• any designator from {children,descendants,sibling,ancestor,all}
• a find()
• a list-based group designator

Such operators are:

• avg_if(scope, condition, expressionStr)
• collect_if(scope, condition, expressionStr)
• if(condition){actions}[else{actions}]
• links[(scope)].directionStr.[linkTypeRegex].attributeNameRefStr
• sum_if(scope, condition, expressionStr)
• while(condition){}