Em Dash: What Is an Em Dash? - The Blue Book of Grammar and Punctuation
https://www.grammarbook.com/blog/dashes/em-dash/
WebEm Dash: What Is an Em Dash? The em dash in American English is a punctuation mark that helps to convey emphasis, introduction, interruption, or a swift change of thought. In doing so, the em dash acts similarly to commas, semicolons, colons, and parentheses.
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