Re: On the masking of undisplayable characters

[Eli Zaretskii]

> Date: Mon, 6 Jul 2015 18:38:13 +0100
> From: <address@hidden>
> 
> I just noticed we have a feature where we use display tables to mask 
> characters
> that cannot be displayed. 

What characters are you talking about, specifically?

> When this happens, it caused me quite a bit of confusion, as I tried to type
> one thing and something else got inserted. I eventually thought of
> investigating the character (which revealed it was being masked by the display
> table), but many users wouldn't know to do this. 
> 
> Could we have a message to let the user know when this happens? Something like
> "undisplayable char being displayed as X". 
> 
> I know this is meant to be helpful, but displaying something different from
> what's in the file is a pretty big deal. I'm not entirely sure it should be
> done without consent, but it definitely shouldn't be done silently. 

It's hard to respond without knowing the details.  Most of the uses of
display tables I know of are there for ages, so adding some kind of
message about that now would seem inappropriate.  (And when exactly do
we display that message? when the character is first displayed?)

Then again, I think you might be over-reacting a bit: Emacs always
displayed special characters specially.  Think about the ^X control
characters, the glyphless-char-display feature, composed characters,
even the newline.  There's nothing new here.