bug#31349: 27.0; Doc of `up-list'

[Drew Adams]

In Emacs 25, apparently, two additional optional args were added to
`up-list'.  But the doc added for the second of these args is not
understandable, to me.

The doc is identical for the doc string and the manual, so going to
either from the other didn't help me understand.

This is the description of the second new arg:

 If NO-SYNTAX-CROSSING is non-'nil' (as it is interactively), prefer to
 break out of any enclosing string instead of moving to the start of
 a list broken across multiple strings.  On error, location of point
 is unspecified.

Looking at the code briefly, it seems to concern not only strings but
also comments.  If so, shouldn't the description mention that?

At any rate, I don't follow the description.  Can you elaborate, perhaps
giving an example?  If I understand the behavior then perhaps I can help
clarify the doc.  Why were these args added?  What use cases do they
serve?

(It's also not helpful or conventional to put descriptions of all args
in the same paragraph.)

In GNU Emacs 27.0.50 (build 3, x86_64-w64-mingw32)
 of 2018-03-21
Repository revision: e70d0c9e66d7a8609450b2889869d16aeb0363b5
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install -C 'CFLAGS=-O2 -static -g3''