[fpc-pascal]Interrupts under Go32

[Shifted Soul]

Hi
I read the documentation about how to write ISRs in Go32.
I found this snip of code :

------!Cut!-------
backupDS : Word; external name '___v2prt0_ds_alias';
------!Cut!-------

(In the Standard units reference manual > The Go32 unit > Hardware
interrupts)
What is "___v2prt0_ds_alias" ? What kind of value it can have ? in which
(external object) file it is found ?