bug#21072: Brave new mark-defun (and a testing tool)

[Stefan Monnier]

>> Regardless of the answer you give above, I'm wondering in which kind of
>> circumstance we'd want to test if we're on "a line containing only
>> a comment".
> You will be surprised, then, that I actually did use a very similar
> function in completely another circumstance: a command that counts
> source lines of code in a region, and excludes lines containing only
> whitespace, comments and docstrings.  (Never mind the discussion about
> whether SLOC is meaningful in any sense;-).)

My point is that it's not very frequent to need this exact definition of
a "comment line" and that there are various other possible definitions
one might need in other circumstances.
So at the very least, the doc should clarify which definition of
"comment line" it uses.


        Stefan