1. override
Constraint operator <=(EquationMember value)

Creates a Constraint by using this member as the left hand side expression and the argument as the right hand side Expression of a Constraint with a Relation.lessThanOrEqualTo relationship between the two.

For example: rightEdgeOfA <= leftEdgeOfB would read, "the entities A and B are stacked left to right."

Source 

@override
Constraint operator <=(EquationMember value) {
  return _createConstraint(value, Relation.lessThanOrEqualTo);
}