What is dnl?

[eric ehlers]

I'm using the documentation at 

http://www.gnu.org/software/automake/manual/html_mono/automake.html

and finding it very frustrating.  For example under "A classic
program" you start using "dnl" without explaining what it means.

In the autoconf documentation, under "8.3.1 Redefined M4 Macros", I
find this definition of dnl:

"This macro kept its original name: no m4_dnl is defined."

Great, that clears it up.

A good rule of thumb when writing documentation is to define a new
term before you use it.  As a very minimum you should define new terms
SOMEWHERE.

- What is dnl?  (I gather it relates to comments - why is it sometimes
used with no comment text, like a carriage return?  How does it differ
from #?)
- Will you be revising your documentation to make it more newbie-friendly?

Thanks,
Eric