bug#59841: 29.0.50; 'before-string' text property doesn't work

[Akib Azmain Turja via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Tue, 06 Dec 2022 00:30:52 +0600
>> From:  Akib Azmain Turja via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>> 
>> The 'Display Margins' node of Emacs Lisp manual says to put
>> 'before-string' on text to use the marginal area (is this the correct
>> term?) while not altering buffer text.  But 'before-string' text
>> property doesn't work.
>> 
>> Steps:  1. Open a clean fundamental mode buffer.
>>         2. (insert (propertize "foo" 'before-string "bar"))
>>         3. The buffer shows only "foo", but not "bar" before it.
>
> The code is incorrect: 'before-string' is an overlay property, not a text
> property.  So you need to define an overlay with a 'before-string' property
> whose value is a string, and put a 'display' property on that string.
>

If that code is incorrect, the 'Display Margins' node of Emacs Lisp
manual is also wrong.  On the fourth paragraph, it says, "put a
‘before-string’ property on the text".

The manual should be clear.

> And if you want the 'display' property to show text in the margin, you need
> also to use set-window-margins to setup the margin.

I know that.

-- 
Akib Azmain Turja, GPG key: 70018CE5819F17A3BBA666AFE74F0EFA922AE7F5
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