HTML5 has been evolving super fast. Not only that, Apple, the driving force (and owner) of webkit, has been making changes as well. In IOS 4.0 a tag called x-webkit-airplay was needed in order to give controls to the video to airplay stream to an Apple TV.
The exact command needed was x-webkit-airplay=”allow”. By default the x-webkit-airplay was actually set to “disallow.” If you wanted your video to have the ability to use AirPlay and stream to an Apple TV you needed to turn it on or “allow” it with the x-webkit-airplay parameter. However, this changed in IOS 5.0. Apple changed the default behavior of x-webkit-airplay to be x-webkit-airplay=”allow.”
So by default if you’re using the video HTML5 tag it will be able to use AirPlay and stream to an Apple TV. You only need to worry about the parameter x-webkit-ariplay if you want to set x-webkit-airplay=”disallow” and not allow streaming over AirPlay to an Apple TV.