Question: How do I say an MXML component is inside some package? Well, it's in a different folder... I know how to do it ActionScript... But when I do in MXML I don't declare the package explicitly because I don't know how, and when I call it to my application, it states that 

> 
> The prefix "package" for element
>  "package:Component" is not bound.
> 
> 
>

Answer: 
Hope this helps.
For a component just create it in a new folder and from your base class when your invoking that component just invoke it with a new namespace.

e.g if you create a new component say employee\_list.mxml in src/component folder

and if you have your main app file ALL\_EMP.mxml in src/ folder then to invoke the component you defined in src/component folder use a namespace as

< mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" **xmlns:Comp="component.\*"** layout="horizontal" >

then you can invoke the component directly in mxml as 
 (tag specific to your App)...

it is somewhat similar to creating and using Taglibs in JSPs...
Check out the [screencast for the Components chapter](http://www.firststepsinflex.com) of First Steps in Flex. It explains this in detail.