function _processProportionalSpacer(context, stackView) {
      context.proportionalSpacerIndex = context.proportionalSpacerIndex || 1;
      var name = '_-' + context.lineIndex + ':' + context.proportionalSpacerIndex + '-';
      context.proportionalSpacerIndex++;
      context.constraints.push({
        view1: name,
        attr1: context.horizontal ? Attribute.WIDTH : Attribute.HEIGHT,
        relation: context.relation.relation || Relation.EQU,
        view2: context.relation.view, // or relative to the stackView... food for thought
        attr2: context.horizontal ? Attribute.WIDTH : Attribute.HEIGHT,
        priority: context.relation.priority,
        multiplier: context.relation.multiplier
      });
      context.relation.multiplier = undefined;
    
      // Add constraint
      for (var i = 0; i < context.prevViews.length; i++) {
        var prevView = context.prevViews[i];
        switch (context.orientation) {
          case Orientation.HORIZONTAL:
            context.prevAttr = prevView !== stackView ? Attribute.RIGHT : Attribute.LEFT;
            context.curAttr = Attribute.LEFT;
            break;
          case Orientation.VERTICAL:
            context.prevAttr = prevView !== stackView ? Attribute.BOTTOM : Attribute.TOP;
            context.curAttr = Attribute.TOP;
            break;
          case Orientation.ZINDEX:
            context.prevAttr = Attribute.ZINDEX;
            context.curAttr = Attribute.ZINDEX;
            context.relation.constant = prevView !== stackView ? 'default' : 0;
            break;
        }
        context.constraints.push({
          view1: prevView,
          attr1: context.prevAttr,
          relation: context.relation.relation,
          view2: name,
          attr2: context.curAttr,
          priority: context.relation.priority
        });
      }
      context.prevViews = [name];
    }
Helper function that inserts proportional spacers (-12%-).
@private