The FAQ of HTML
Is there a difference between *.html and *.htm?
No not really. They are both HTML-extensions. The only difference is that a server can "turn off " one of the 2. So it is not recognized. This rarely happens.
Does UPPER-CASE and lower-case matters in HTML?
No, not in HTML but ...
It does matters in filenames. Now windows (2000|NT) do not see any differences. But Linux and Unix do. I, personally, write everything in lower-case. Javascript and definitely java-Applets are very sensitive for UPPER- and lower-cases. So use one of the 2, but don't start to mix.How do I add special characters?
Special characters, like <, &, ®, "e; have to be replaced by a code in HTML. Here is a list of all special characters and there code.