The browser will recognise them if:
1 - the document is written in UTF8 encoding
2 - the document is served(response headers) to the browser with the encoding UTF8 [1
3 - the document have the <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
The browser will maybe display "squares", maybe with codes in it (firefox), if you don't have the required fonts to display these correctly. Found some maybe at the bottom of this page: http://www.wikipedia.org/
The browser will display mojibake
when fails to render these correctly because of an encoding issue.
You just type every character you need (letters and non-letters), and when typing &, <, >, ", ' just type &, <, >, ", ' instead.
", ' is usefull in case like this one:
<a href="<?php echo $url?>"></a>
<a href='<?php echo $url?>'></a>
which can be translated as:
<a href="http://d.tld" onclick="hack()
<a href='http://d.tld' onclick='hack()