On the masking of undisplayable characters

[<bruce.connor.am@gmail.com>]

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I just noticed we have a feature where we use display tables to mask
characters that cannot be displayed.

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.

Artur

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