Why does IE require attributes classid and codebase to properly embed Flash?

Recently struggling with weird IE9 + Flash problem I came over multiple advices to use classid and codebase attributes specifically for IE. But couldn't find any explanation of why they might be required or what they simply do. Any good writeup on this topic anywhere?

Side-question:

Can I just make classid value up out of my head or it should be generated ac开发者_开发知识库cording to some rules?

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These attributes let the IE know which registered activex control with specific version need to be invoked for displaying flash file. The details about codebase and classid can be found in below links :

http://msdn.microsoft.com/en-us/library/ms533559%28v=vs.85%29.aspx

http://msdn.microsoft.com/en-us/library/ms533576%28v=VS.85%29.aspx