[XeTeX] :letterspace oddities

[Jonathan Kew]

On 25/8/16 18:02, Philip Taylor wrote:
> For some time now I have been partially aware of some oddities in the
> XeTeX implementation of :letterspace, but it was only today that my
> thoughts crystallised sufficiently for me to attempt to record them on-
> list :
>
> 1) Search functionality.
>
> For :
>
> \font \errorfont = "Copperplate Gothic Bold:letterspace=8,color=BF0000"
> scaled 2260
>
> \newbox \errorbox
>
> \setbox \errorbox = \leftline {\errorfont +++ NOT AT TOP OF PAGE +++}
>
>
> Adobe Acrobat 7.1 has no problem locating the string "+++" if the
> contents of \errorbox end up in the PDF file; however, for
>
>
> \font \errorfont = "Copperplate Gothic Bold:letterspace=16,color=BF0000"
> scaled 2260
>
> the same string cannot be found.

Remember that TeX doesn't treat spaces as "characters" but as glue, 
which means they don't end up as part of the *text* in the resulting DVI 
or PDF file; they are merely implied by the positioning of the visible 
glyphs.

As a result, consider what Acrobat must be doing: it can "see" the 
visible glyphs and their positions, but it "sees" no <space> characters 
separating words. It must be inferring which characters are adjacent in 
the text stream, and which are separated by spaces, purely from their 
positions. So when you add a substantial amount of letter-spacing, it 
seems likely that Acrobat will view the text as being "+ + +" rather 
than "+++".

It's possible that \XeTeXgenerateactualtext=1 would help, as I think it 
would annotate the letter-spaced "+++" as a unit with its actual text, 
allowing Acrobat to find it correctly despite the intervening spaces 
that *appear* to be present from just looking at the glyphs.

JK