this is better but i worry it'll lead to confusion.

why can't we just use  `{@size key=myValue}`   key points directly to the 'foo' and you don't run through the string interpolation function.

We are assuming that myValue is always a string. what about `{myValue: [1, 2, 3], myValue2: function(){return false}}`   which I believe would return '1,2,3'.length  which is not expected. I don't know what myValue2 would do.