What I've been saying is that an em dash can be used for making parenthetical comments -- like an appositive -- whereas you said that was an improper usage.
According to the article you provided and bolded, an em dash isn't necessarily a proper replacement for an appositive. It's a "sudden break in thought," whereas an appositive doesn't follow this pattern. It is a much more expected elaboration, such as this statement I am typing right now.
In grammar, an appositive is a noun phrase that renames or describes another noun phrase, with no word interposed between the two phrases. So, Alice in Bill's friend, Alice,... is an appositive noun phrase; Alice in Bill's friend, whose name is Alice,...
I don't think it's a valid replacement, but dashes definitely have their uses in papers...
Well my AP Lit teacher edited it and said it was really good and that she was impressed. There were some punctuation errors, and she replaced some dashes with commas but the George W. Bush one at the top is fine but I do need to add a closing one.
Pffff! She's wrong! Change it!
Haha, kidding. I do think that an appositive is more appropriate, though.