Custom grammar

custome tag's concept is same with directive in Angular in essence,but the difference is that riverjs tag can olny be attributes of element and the declaration of tag must under river.grammer namespace, for example I want to write a plugin for showing the correct date formate, you can do it like this;

example:

<div scope="datetime.ctrl">
  <p>{{time}}</p>
  <p datetime="time"></p>
</div>

define('river.grammer.datetime',function(exports,require,module){
  //notic the namespace river.grammer, here is a typo, not grammar
  exports = module.exports = datetime;

  function datetime(str,scope,element){
    //str is the value of your custom attribute 
    //here we use it as parameters for searching data in scope
    var key = str;
    element.innerHTML = (new Date(scope[str])).toLocaleString();
  }
})

controller

define('datetime.ctrl',function(exports,require,module){
  exports.time = '2014-03-18T07:19:20.047Z';
})

pre-build process

firt you need to install riverjs from npm
```
  npm install -g riverjs
```

second switch path to your work home

  cd myapp
  mkdir detatime grammar
  touch datatime/ctrl.js
  touch grammar/datetime.js

riverjs ask directive must under river.grammar namespace,in pre-build process the alais grammar replace it.so we make a grammar folder and all modules in grammar folder will be directive. you can change to other folers by edit river.json alais property

write down source without define function

datetime/ctrl.js

//notic the namespace river.grammer, here is a typo, not grammar
exports = module.exports = datetime;

function datetime(str,scope,element){
  //str is the value of your custom attribute 
  //here we use it as parameters for searching data in scope
  var key = str;
  element.innerHTML = (new Date(scope[str])).toLocaleString();
}

grammar/datetime.js

  exports.time = '2014-03-18T07:19:20.047Z';

build at root path
```
  cd myapp
  riverjs build .
```