In an even more perfect world you can update the preview, like on SquareSpace. Their preview is editable and (though it's been years so can't exactly recall) I think you can update right from it.
While I don't object to it, at that point I start to wonder what the difference is between that and the WYSIWYG view. (Also, implementing that is, I suspect, much, *much* harder: in most important respects, it *is* essentially implementing a new version of the WYSIWYG editor.)
The memory load with pop-up previews (like they do now on Wordpress.com - which I think is actually more like the lightbox discussed above) is considerable; all the page features of the preview are sluggish and it just slows everything down).
While I can believe that's true in some implementations, there's no reason why that should be generally true. Doing a dynamic keystroke-by-keystroke preview is going to add some load, sure, but a simple preview pane (either side-by-side or lightbox) shouldn't add much; that just suggests bad implementation...
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While I don't object to it, at that point I start to wonder what the difference is between that and the WYSIWYG view. (Also, implementing that is, I suspect, much, *much* harder: in most important respects, it *is* essentially implementing a new version of the WYSIWYG editor.)
The memory load with pop-up previews (like they do now on Wordpress.com - which I think is actually more like the lightbox discussed above) is considerable; all the page features of the preview are sluggish and it just slows everything down).
While I can believe that's true in some implementations, there's no reason why that should be generally true. Doing a dynamic keystroke-by-keystroke preview is going to add some load, sure, but a simple preview pane (either side-by-side or lightbox) shouldn't add much; that just suggests bad implementation...