I don't really know what you are trying to get at. Almost every front-end framework is going to have some type of "proprietary syntax" -- that's basically what

I don't really know what you are trying to get at. Almost every front-end framework is going to have some type of "proprietary syntax" -- that's basically what a framework is. Even backend templating languages have custom syntax that must be learned. Otherwise, I guess there is jQuery or web components if you are only supporting modern browsers.