I'm confused about that. you mean a pop-up window? A small window which explains the larger window, which it now partially obscures?

If the explanation is small enough, it should go on the page it's explaining. If it's too large, it should be on a page of its own, and let the user read it and go back.

Or of course you could redesign the first page so that it needed less explanation.

Every time someone argues for usability guidelines like "don't mess with the user's browser", someone else says "Except in my special case, that's right. But I can ignore that rule because..."

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 =~y~b-v~a-z~s;                             print
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