nl_tokens: $foo . bar 属性求值，最后面两个参数在用户传递的函数中用到
pl_tokens: function ( property , baseRef , ast ) { // fix #54 if ( baseRef === null || baseRef === undefined ) { return undefined ; } /**
         * type对应着velocity.yy中的attribute，三种类型: method, index, property
         */ var type = property . type ; var ret ; var id = property . id ; if ( type === 'method' ) { ret = this . getPropMethod ( property , baseRef , ast ) ; } else if ( type === 'property' ) { ret = baseRef [ id ] ; } else { ret = this . getPropIndex ( <mask> , baseRef ) ; } return ret ; }