bug#3400: bug in add-text-properties

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> If you hit `b', the `b' will be inserted right before "12345", and it
>> will not be invisible.
> So what?  With `C-x =' I see `A' and get the data of `1',

Point is at position 1 (i.e. just before the char "1" rather than
before the char "A"), so it makes sense for C-h = to return data about
that position rather than about some other position one line down.

Also it makes sense to draw the cursor over the "A" because there's
nowhere else to draw it.  Basically, since the chars "12345\n" are
invisible and intangible, the display should pretend they don't exist,
but C-x = is designed to show you the actual underlying data.

> Actually, there is no way to retrieve information from `A' at all.

Your `intangible' span basically requests "12345\nA" to be treated as one
indivisible entity, so it's indeed difficult to get info about most of
those individual chars.

>> BTW, why are you using `intangible'?
> I've just copied some code -- I haven't checked whether I can omit it.

First things first: if you're not 200% sure you absolutely need
`intangible', then don't use it.  It's a nasty beast.


        Stefan