Definition of "rule"?

The CSS1 spec defines a "rule" as "a declaration and its
selector."

So, given this style sheet:

H1, H2, H3: { color: white; background: blue; }

is that one rule, two rules, three rules, or six rules?
I'm fairly new to style sheets and in reading through the spec,
I couldn't determine from the section on grouping or from
context what the correct answer is.

I'm also stunned by how wildly different a style sheet
can be interpreted by Navigator 4.01, IE 3.02, and IE 4.0 platform
preview 2 on my Windows 95 system.  It seems very
discouraging, since seemingly innocuous style sheet rules can
cause portions of a page to not be displayed at all.
-- 
E. Stephen Mack <estephen@emf.net>    http://www.emf.net/~estephen/