i have not read it all but it seems there is no rules how variable name has to start and how not..which means this article doesnot include all rules about variables and may be there is some more rules.
We are in the process of rewriting this content:
I think that http://www.adobe.com/devnet/actionscript/learning/as3-fundamentals/var iables.html will answer your questions.
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Adobe Systems Incorporated
Standard typical practice can be used for c-esque languages and variables.
Some typical guidelines are:
Getting your variables and method names to read like a sentence is the ideal goal. You want to be able to return to old code, or someone else's code, and not spend a huge amount of time figuring it out.
As a side note, not related to naming, always try to set the type of your variable. By doing that you can track down bugs when the compiler tells you you can't assign a letter to something that should be a number. It also keeps the compiler speedy never needing to worry about dynamic type casting. If you specify no type or a dynamic type (*) it's very hard to track down errors (like in AS2).
Those are the basics of any language. The only real difference is some languages require a dollar sign to designate a variable (PHP, etc) or another character for type (Perl, etc). ActionScript is pretty loose.