how make IIDs?

[buva]

soryy .my english abillity not so good...
 i understand IIDs. but i want to know how make IIDs in mozilla.
i be worked htmlparser to create tag but it is xml. i saw thatl modules of
mozilla use xpcom then i think that htmlparser  use xpcom...
 all classes and interfaces are assigned unique IDs. i want to use IIDs and
to create...
but i don't know it....
please tell me how create IIDs