N is for Namespaces in MXML

If you want to use custom components (outside of the mx or flash packages) in your Flex application, first you'll have to setup a namespace to tell Flex where to find your custom controls. (Using custom controls in your MXML can be a little tricky at first.)

   xmlns:mycontrols="my.custom.controls.*"
>

Learn more about MXML Namespaces at Flex After Dark...