Unexplained code in "Classroom in a Book" on AS3

Question

I'm slowly going through the Adobe "Classroom in a Book" on
ActionScript. Every now and then the sample code includes what
appears to be a property "e" as in "function doThis (
e:mouseEvent)" or "var rbg:RadioButtonGroup =
e.target as RadioButtonGroup;"
What is "e", and when should one use it?
Thanks.

Answer 1

From the description you give, that "e" is in my opinion by
99% an event variable/object.
function (e:Event) { trace(e); } // defines 'e' as an object
of type Event.
The same way you can write:
function (myvariable:Event) { trace(myvariable); } or
function (microEvent:Event) { trace(microEvent); } or
whatever.
In each case that means that the function take one argument
of type Event.
Depending the case, you can use MouseEvent type, IOErrorEvent
etc. etc. Each type of event contains different information. But
all events contain i.e. the target property to find out from where
the event started.
I also always use variable 'e' for defining event variables
to handler functions. Because:
a) 'e' is to short to type :P
b) doesn't require any time to think it's name in order to be
appropriate to the code :P
c) that kind of variable is very common in use. Every event
handler function have one such variable.
Thus why to use any other names to describe them, except from
just the fast, easy, understandable 'e'? :P
I.e. Suppose you have write a code with 20 event handlers
like:
function check_sex(e:Event) { if (e.target.name="woman") {
UseAMan();} else { UseAWoman();} }
function ioerror_handle(e:IOEventEvent) { e.target.Reload();
trace (e.text); }
function on_progress(e:ProgressEvent) { slider.width =
e.bytesLoaded/e.bytesTotal; } etc
You can easily use any other variable name instead of 'e'.
However if you do that, you will type much more letters + the code
might be a bit more confusing to understand for someone else!....
:P lol... :D I gotta to sleep.. 'e'e'e'ee....