buildLoop = function(index, len) {
                        var isConditional = conditional !== undefined;
                        return {
                            index: index+1,
                            index0: index,
                            revindex: isConditional?undefined:len-index,
                            revindex0: isConditional?undefined:len-index-1,
                            first: (index === 0),
                            last: isConditional?undefined:(index === len-1),
                            length: isConditional?undefined:len,
                            parent: context
                        };
                    }
For type logic tokens.

 Format: {% for expression %}