distribution version numbering

[Aurelio Turco <azt@bom.gov.au>]

According to http://www.debian.org/doc/debian-policy/footnotes.html,
an increment in the last component of the version number (eg: 3 in 2.2r3)
means "only security fixes and other major bug fixes".

As for the meaning of an increment in any of the other two components
I have not been able to find any documentation.

Could some kind soul outline what the meaning of an increment in the
other two components is, or point me to the relevant documentation?

Cheers.
Aurelio.

PS: I take it that a major change = a change in the first component,
      a minor change = a change in the second component &
      a revised change = a change in the third component?