GNU bug report logs - #30816
27.0.50; Info documentation of previous-property-change is not very clear

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Xu Chunyang <mail <at> xuchunyang.me>
To: bug-gnu-emacs <at> gnu.org
Subject: 27.0.50;
 Info documentation of previous-property-change is not very clear
Date: Wed, 14 Mar 2018 17:58:32 +0800

(info "(elisp) Property Search") has the following:

     -- Function: previous-property-change pos &optional object limit
         This is like ‘next-property-change’, but scans back from POS
         instead of forward.  If the value is non-‘nil’, it is a position
                                 ^^^^^^^^^
         less than or equal to POS; it equals POS only if LIMIT equals POS.
                                    ^^

I don't understand the second sentence. What "the value" stands for? If
it stands for LIMIT, what "it" stands for?

Message #8 received at 30816 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Xu Chunyang <mail <at> xuchunyang.me>
Cc: 30816 <at> debbugs.gnu.org
Subject: Re: bug#30816: 27.0.50;
 Info documentation of previous-property-change is not very clear
Date: Wed, 14 Mar 2018 18:26:46 +0200

> From: Xu Chunyang <mail <at> xuchunyang.me>
> Date: Wed, 14 Mar 2018 17:58:32 +0800
> 
> 
> (info "(elisp) Property Search") has the following:
> 
>      -- Function: previous-property-change pos &optional object limit
>          This is like ‘next-property-change’, but scans back from POS
>          instead of forward.  If the value is non-‘nil’, it is a position
>                                  ^^^^^^^^^
>          less than or equal to POS; it equals POS only if LIMIT equals POS.
>                                     ^^
> 
> I don't understand the second sentence. What "the value" stands for?

When we say "value" in the context of describing a function, we mean
the value the function returns.  In this case, the value returned by
previous-property-change.

> If it stands for LIMIT, what "it" stands for?

"It" stands for the value returned by the function.  the text says
that the function returns the position of the previous change of the
property, and that position could only be the same as the starting
position POS if LIMIT is equal to POS, i.e. if LIMIT forces the
function to stop at its starting position.

I hope this clarifies the issue.

Message #11 received at 30816 <at> debbugs.gnu.org (full text, mbox):

From: Xu Chunyang <mail <at> xuchunyang.me>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 30816 <at> debbugs.gnu.org
Subject: Re: bug#30816: 27.0.50;
 Info documentation of previous-property-change is not very clear
Date: Thu, 15 Mar 2018 03:04:30 +0800

Eli Zaretskii <eliz <at> gnu.org> writes:

>> From: Xu Chunyang <mail <at> xuchunyang.me>
>> Date: Wed, 14 Mar 2018 17:58:32 +0800
>> 
>> 
>> (info "(elisp) Property Search") has the following:
>> 
>>      -- Function: previous-property-change pos &optional object limit
>>          This is like ‘next-property-change’, but scans back from POS
>>          instead of forward.  If the value is non-‘nil’, it is a position
>>                                  ^^^^^^^^^
>>          less than or equal to POS; it equals POS only if LIMIT equals POS.
>>                                     ^^
>> 
>> I don't understand the second sentence. What "the value" stands for?
>
> When we say "value" in the context of describing a function, we mean
> the value the function returns.  In this case, the value returned by
> previous-property-change.

I see. I notice the term "the return value" is also used in some place
in the manual.

>> If it stands for LIMIT, what "it" stands for?
>
> "It" stands for the value returned by the function.  the text says
> that the function returns the position of the previous change of the
> property, and that position could only be the same as the starting
> position POS if LIMIT is equal to POS, i.e. if LIMIT forces the
> function to stop at its starting position.
>
> I hope this clarifies the issue.

Thanks for your explanation. Feel free to close the issue.

Message #16 received at 30816-done <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Xu Chunyang <mail <at> xuchunyang.me>
Cc: 30816-done <at> debbugs.gnu.org
Subject: Re: bug#30816: 27.0.50;
 Info documentation of previous-property-change is not very clear
Date: Wed, 14 Mar 2018 21:35:39 +0200

> From: Xu Chunyang <mail <at> xuchunyang.me>
> Cc: 30816 <at> debbugs.gnu.org
> Date: Thu, 15 Mar 2018 03:04:30 +0800
> 
> Thanks for your explanation. Feel free to close the issue.

Done.

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