Interestingly, in the actual example he uses that isn't a fixed with element. Look at the Heroku.com site, its the div with id "accordion". That space to the left of it is created because of the padding of the surrounding div (which is fluid width), and the margin of the accordion div.

Its sister element with id "rightelement" is actually fixed width, but I don't see the issue there since the majority of its contents are image elements and not text.

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That said, I agree with you set a max-width for text only enclosures, and a min-width for enclosures that have image elements.