How does the Browser determine what version to load, (HTML5 or SWF)

Hi Folks,

I know the simple answer to this question but what I really need to know is what is the order the browser loads the versions, for example does it check to see if SWF is present first and load that,  or does it load the HTML first,  if both versions are available?

I am working with a client whose LMS requires both versions, my preference would be to design for the HTML5 version but if most browsers loads SWF first,  then some features would not work in the the SWF version. 

Is there any logic to browser version selection?

Cheers

Steve