Re: How to use display text property with after-string?

[Marcin Borkowski <mbork@mbork.pl>]

On 2016-10-21, at 09:35, Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Marcin Borkowski <mbork@mbork.pl>
>> Date: Fri, 21 Oct 2016 08:15:31 +0200
>> 
>> --8<---------------cut here---------------start------------->8---
>> ;; this is a comment
>> 
>> (put-text-property 14 21 'display '(after-string " which is cool!"))
>> --8<---------------cut here---------------end--------------->8---
>> 
>> After C-x C-e with point at the end, I see this:
>> 
>> --8<---------------cut here---------------start------------->8---
>> ;; this is a comment
>> 
>> (put-text-property 14 21 'display '(after-string " which is cool!"))
>> --8<---------------cut here---------------end--------------->8---
>> 
>> but I expected this:
>> 
>> --8<---------------cut here---------------start------------->8---
>> ;; this is a commentcomment
>> 
>> (put-text-property 14 21 'display '(after-string " which is cool!"))
>> --8<---------------cut here---------------end--------------->8---
>> 
>> What am I doing wrong?
>
> The 'display' property doesn't support after-string, only the overlay
> properties do.

I see.  I was a bit afraid that is the case.

Is there any other way to put some nonexistent text in the buffer?
Overlays are not very good that, since I hear many overlays in a buffer
may slow things down.  My use case is as follows: I want to write
a function which will find all the dates in the US format (M/D/Y) in the
buffer and put a date in a sane format (maybe together with something
like "3 days ago" or "tomorrow") next to them.  (That would be very
useful for me, since I sometimes get emails from Americans, and dealing
with dates in M/D/Y format is a huge cognitive load for me;-).)

TIA,

-- 
Marcin Borkowski