When I do my alt tag, am I supposed to put a code in for symbols - example - alt="cat & dog" .... should I put the &, or put the amp&; in place of the &. My real life situation is using the dollar sign. That's what brought my question up. Basically I want to know if it is okay to use alt="on sale for $5" ... or put something else in place of the "$". Do you get what I mean? - I'm using wordpress, so does any of this ish even matter?
Normally, as long as you use double quotes, no, it doesn't matter. It might fail on validation, but this is not a critical error - it's mostly useful if you're using XHTML strict, then it might actually break the page. If you're using HTML 5, it doesn't matter - although, if you want the page to validate 100%, then you need to use proper HTML Code - you'll find a good list here: http://www.ascii.cl/htmlcodes.htm
The reason why the ampersands (&) have to be escaped is that they are used to identify and call predefined character entities. To do so, just use "&". As for some other special characters, there's a potential ambiguity between their literal meaning and their function within the given document type. For instance, the dollar sign is used to declare and call variables in php, the language wordpress uses. Therefore it's not such a bad idea to escape it ( use $ ). ...though in practice it makes no real difference, given how broken and stupid wordpress is in the first place. This particularly applies if you're under html5 doctype, as it behaves like honey badger. It just doesn't care (sigh)...