TechWhirl (TECHWR-L) is a resource for technical writing and technical communications professionals of all experience levels and in all industries to share their experiences and acquire information.
For two decades, technical communicators have turned to TechWhirl to ask and answer questions about the always-changing world of technical communications, such as tools, skills, career paths, methodologies, and emerging industries. The TechWhirl Archives and magazine, created for, by and about technical writers, offer a wealth of knowledge to everyone with an interest in any aspect of technical communications.
-------------------- END OF ORIGINAL MESSAGE --------------------
Ah, but is it? "Which" can be correctly used in non-restrictive AND
restrictive clauses (vs. "that," which is used only in restrictive
clauses). Inserting a comma changes the implied meaning of the sentences.
Take for example:
The lawnmower which is in the garage is broken.
(There's more than one lawnmower, and it's the one in the garage that
we're talking about.)
The lawnmower that is in the garage is broken.
(Same meaning as the above example)
The lawnmower, which is in the garage, is broken.
(There may or may not be other lawnmowers. The fact that the broken
one is in the garage is simply extra information -- the main point is
that the lawnmower is broken.)