No matter for text processing or for displaying/understanding purposes, we often need to know where a quotation of text begins and where it ends. Unicode LEFT SINGLE/DOUBLE QUOTATION MARK can serve as the left tag, while the right SINGLE/DOUBLE QUOTATION MARK serve as the right tag.
For ASCII, to quote a text, grave accent (0x60) serve as a left quotation mark together with apostrophe (0x27) served as the corresponding right quotation mark(as in `quote'), but https://www.cl.cam.ac.uk/~mgk25/ucs/quotes.html is not suggesting this way, as the author tells "Your text will otherwise appear rather strange with most modern fonts", so for ascii, we quote a text using ' or " pairs while we must try our best to tell a apostrophe is a start or end.
