These are the characters made with the ampersand &, then # and then a number, terminated with a semcolon.
For example ¾ produces the fraction ¾
It seems as though there are a huge amount of numbers that can produce all kinds of symbols such as: mathematical; obscure alphabets (e.g. Myanmar); the Braille alphabet, etc.
How come some of these codes work and yet others don’t ?
Is it browser settings or something to do with Unicode standards?
It’s a little of both (plus some other things.)
Not all browsers are set up to properly handle Unicode characters, and even if they are, the machine may not have the correct Unicode fonts installed.
Another problem is that a web server may tell the browser that a given page is in an extended ASCII encoding like ISO-8859-1 (our familiar Latin-1 encoding) even if the data contains Unicode characters. In this case, the browser won’t know what to do and different browsers make different guesses on how to proceed. This can be solved with proper web server configuration, but often the administrator is not aware of the problem.