As far as I can tell, they play pretty much the same role. They emphasise text. The default rendering of <strong> is bold text and the default for <em> is italic, so which one I use depends on whether I would use bold or italics if I were writing for print.
IMHO, the StackOverflow distinction is an overly ambitious attempt to draw a distinction that isn’t there … although it does seem consistent with the examples presented in the SitePoint Ref:
I guess if that distinction works for you, then go with that. Personally, I don’t think I will. If I would use italics for a group of words in print, I would use <em> on the web to indicate the emphasis on all of those words.
<em> and <strong> have remained pretty much the same, there has been a slight realignment in their meanings.
In HTML4 they meant ‘emphasis’ and ‘strong emphasis’. Now their meanings have been differentiated into <em> representing stress emphasis (i.e., something you’d pronounce differently), and <strong> representing importance.
The Stack Overflow answer is mainly irrelevant; since it is actually relating to HTML5, which is not a fully normative markup language unlike HTML 4.01 thus you cannot compare the two… other than HTML 4.01 actually is a recommendation and supported by legacy browsers.
It may have helped if originally it was made clear as mud you were after the Fred5 draft reformulation or to which markup you were attempting to apply it to because that then determines as to whether the #1 quoted text has any value or nought!
However, let’s for one moment assume for hypothetical idiocies sake we were talking Fred (#1) then under those conditions; EM would be ‘stress emphasis’ and ‘changes the meaning’ whereas STRONG would be ‘strong importance’ and ‘does not change the meaning’.
In which case my answer #4 is still fully correct and only in context (of a differing draft) would #1 be of any value.
Earlier this year there was a discussion about the 5 being removed from “HTML5”, and somehow out of that discussion arose the suggestion that HTML5 should be called “Fred”. I think xhtmlcoder is fixated on it because he’s desperate not to have to change his username to html5coder. (Mind you, it sounds better than Fredcoder to me.)
Ralph, I wouldn’t need to change my username I don’t use such non normative markup plus the five is officially dead but FredCoder sounds like some real retro dark horse! Far more awesome than htm5coder or html5 anything… in the URL.