Your editors are displaying the offending character, you're just not recognizing it. The code point in the error message refers to the left double quotation mark character, which is indeed present in some examples on the linked page. This is almost certainly an unintentional effect of some well-meaning text editing software. As you correctly point out, code examples are intended to be copied and pasted, and you should report a bug to the site admins.
To add to the confusion, the error message printed by Seed's JavaScript parser is wrong: it misrepresents the \u201c
character (which has decimal code 8220) as \u8220
. This is why attempts to search for \u8220
fail.
To fix the problem in your file, you need to replace the character with an upright quotation mark. To search for an arbitrary Unicode character in a GTK-based text editor, press ctrl-f to initiate search and input the character by with ctrl-shift-u followed by the code point, in this case 201c
. You will need to do the same for the right quotation mark, whose hex code is 201d
.