The native modifier indicates that a function is somehow implemented natively or by the host environment, and only the signature is provided in script.

To be honest this is not very useful in typical web development, since there is no way to cal native functions anyway. It is used internally in Mascara, but there is no further support for it.

When a function is prefixed with native, it does not provide a function body:

native function formatHarddisk(destroyPhysical : boolean) : void;