code: function(el, value)
  	{
  		// TODO Restrict to text input fields?
  		
  		if (el.cbRestrict)
  		{
  			el.removeEventListener('keypress', el.cbRestrict);
  		}
  		
  		el.cbRestrict = function(event)
  		{
  			if (event.ctrlKey)
  			{
  				return;
  			}
  			
  			var code = event.keyCode || event.which;
  			var char = event.key || String.fromCharCode(code);
  			var regExp = value;
  				
  			if (!conbo.isRegExp(regExp))
  			{
  				regExp = new RegExp('['+regExp+']', 'g');
  			}
  			
  			if (!char.match(regExp))
  			{
  				event.preventDefault();
  			}
  		};
  		
  		el.addEventListener('keypress', el.cbRestrict);
  	}
docs: Restricts text input to the specified characters
  
  @param 		{HTMLElement}	el - DOM element to which the attribute applies
  @param 		{string} 		value - The value referenced by the attribute
  @returns		{void}
  
  @example
  <div cb-restrict="propertyName"></div>