what does => mean when it appears in C #pragma directive?

I am reading KN King 'C Programming A Modern Approach"

In the section on 'The #pragma Directive' it says this:
Quote:

The #pragma directive has the form '#pragma tokens' where tokens are arbitrary tokens. #pragma directives can be very simple (a single token) or they can be much more elaborate:

Code:#pragma data(heap_size => 1000, stack_size => 2000)What does => mean in this context? Is the author arbitrarily defining his own token? Also what does this particular directive actually mean/do?