I was just discussing the emergence of HTML 5 with a colleague and he explained that the introduction of HTML 5 would mean some changes to the syntax and the semantics of the language’s elements and attributes. For instance, HTML can be written in two syntaxes: HTML and XML.
From my experience I can say for certain that using XML will enable more complex webpages that will run faster on Web browsers. I also learnt that XML requires a stricter, more accurate grammar than HTML and thus requires less work by the local computer to run quickly and correctly. There is a but though, XML pages require more work by the developer to achieve the higher accuracy level.
I will need to read up more on this and post about it.