bug#64016: 29.0.91; Fix some Texinfo markup in manuals

[Eli Zaretskii]

> Date: Mon, 12 Jun 2023 15:09:41 +0100
> From:  "Basil L. Contovounesios" via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> I attach a patch intended for emacs-29, which primarily marks up nil/t
> in the manuals as @code (I noticed some instances of @var{nil} while
> reading the corresponding text).
> 
> WDYT?

LGTM, thanks.  Just a few minor nits:

> --- a/doc/lispref/modes.texi
> +++ b/doc/lispref/modes.texi
> @@ -2921,13 +2921,13 @@ Imenu
>  return non-@code{nil} if the node is a valid node for @var{category},
>  or @code{nil} if not.
>  
> -@var{category} could also be @code{nil}.  In which case the entries
> +@var{category} could also be @code{nil}.  In this case the entries

Here' I'd just convert the period int a comma:

  @var{category} could also be @code{nil}, in which case the entries

Because the change you sggest doesn't make this a better English,
AFAIU.

> --- a/doc/misc/ede.texi
> +++ b/doc/misc/ede.texi
> @@ -1900,7 +1900,7 @@ ede-cpp-root-project
>  @end deffn
>  
>  @deffn Method ede-cpp-root-header-file-p :AFTER proj name
> -Non @code{nil} if in @var{PROJ} the filename @var{NAME} is a header.
> +Non-@code{nil} if in @var{PROJ} the filename @var{NAME} is a header.
                        ^^^^^^^^^^              ^^^^^^^^^^
Argument of @var should always be in lower case.

>  @defvar eudc-ignore-options-file
> -If non-nil, then EUDC ignores @code{eudc-options-file} and warns or
> -issues an error when an attempt is made to use it.  Most users should
> -set this, and keep their EUDC configuration in the main Emacs
> -initialization file instead.  The separate eudc-options file has
> -created confusion for users in the past.
> +If non-@code{nil}, then EUDC ignores @code{eudc-options-file} and
                      ^^^^
That "then" is redundant, and should be dropped.

> @@ -878,11 +878,12 @@ Proc customization variables
>  @item flymake-proc-diagnostic-type-pred
>  A function to classify a diagnostic text as particular type of error.
>  Should be a function taking an error text and returning a diagnostic
> -symbol (@pxref{Flymake error types}).  If non-@code{nil} is returned but
> -there is no such symbol in that table, a warning is assumed.  If nil
> -is returned, an error is assumed.  Can also be a regular expression
> -that should match only warnings.  This variable replaces the old
> -@code{flymake-warning-re} and @code{flymake-warning-predicate}.
> +symbol (@pxref{Flymake error types}).  If non-@code{nil} is returned
> +but there is no such symbol in that table, a warning is assumed.  If
> +@code{nil} is returned, an error is assumed.

How about fixing the abuse of passive voice here, while you are at it?