Isn't the old syntax what Roxen uses to mix different quotes in the same attribute value? I believe it's supposed to work like this:
<foo attr="use ' here"'use " here'/>
I do not really think that was ever an encouraged syntax? "e; has always been preferably to my knowledge. It has been a while, however.
And it is an issue if you want Parser.HTML to parse actual HTML. Since the 'save a space' seems to be surprisingly common, granted, we only encounter issues in our turbo servers when it is used with "style" or "src", but that happened fairly often, presumable because 'style' has a tendency to contain whitespaces.