In http://html5please.com the each features listed by saying use with Polyfill or Fallback. I was wondering what is the different both? kindly help me in understanding the different.
Thanks in advance.
Polyfill replaces the feature with the same functionality but implemented with supported technologies, so you're still able to use the same API as in new browsers. For example, classList only supported starting from IE10, but you can add a script written in js that adds a classList object to any dom element so you don't need to rewrite your code to detect a browser or a feature.
Fallback usually replaces the feature with simplified functionality or third-party plugin or even error message. For example, if the browser does not support video tag, you can replace it with a flash plugin.
UPD: You can also check this question for more information.