Pressure regulators

In the code check book it states:

Expansion tank required for regulators w/o integral bypass.

My question is what are the pertaining to when they state w/o integral bypass.

How would I know if the regulator has or does not have a integral bypass.

Thanks

See this thread, especially starting at about page 3

http://www.nachi.org/forum/showthread.php?t=27209