In theory this was nice, but having actually dealt with it in production IE had all sorts of weird bugs with it. Mixing JScript & VBScript (much less PerlScript!) in ASP was even worse, the order of execution of the different language blocks was not specified and could change in a point release or even between installations. In practice both in the browser and on the server Microsoft's multiple language support wasn't really suited to mixing them.
But ASP pages have nothing to do with IE the browser since that was a server-side technology. I mixed JScript and VBScript without problems for a long time in an application I maintained.
