Re: @U{xxxx} -- some TeX characters with a capital don't seem to work

[Benno Schulenberg]

Op  4-07-2017 om 18:41 schreef Gavin Smith:
> On Tue, Jul 04, 2017 at 10:25:39AM +0200, Benno Schulenberg wrote:
> > So... what that section of texinfo.tex does is: translate a code
> > to a named texinfo character?  But where are these texi characters
> > defined?  Because, for example, @U{25B3} works, producing a triangle,
> > but I can't find @triangle anywhere in texinfo's code?  Where does
> > it come from?
>
> It is built into TeX (or more precisely plain TeX). This file is called
> plain.tex. On my computer, it is located
> at /usr/share/texmf/tex/plain/base/plain.tex, but may be elsewhere
> depending on how TeX was installed.

For me the file is:
  /usr/share/texlive/texmf-dist/tex/plain/base/plain.tex

It says:
  \mathchardef\triangle="0234

But what is that code, 0234?  It isn't Unicode.  So what is it
referring to?

> The problem with supporting a filled diamond is that there seems to be
> no glyph in the default set of fonts for TeX that corresponds to that
> symbol. That's about as far as we can go with Unicode support.

It seems that XeTeX can use any Unicode character:
  https://en.wikipedia.org/wiki/XeTeX

Now the question becomes: how do I tell pdftex to use xetex?

> > \diamond is already used for U+22C4 and \diamondsuit for U+2662.
>
> The diamond suit glyph is slightly different as it is more elongated in
> a vertical direction whereas the diamond symbol appears to be a square
> resting on one corner. There's probably no harm in using \diamond for
> both U+22C4 and U+25C7.

I don't think that is a good idea.  If I specify a certain code,
and later copy-paste something out of a document and get a different
code... that's not good.

But it appears that copy-pasting out of a PDF does not work for
most special characters.  A bullet works, but an "ê" becomes "^e "
and "△" becomes "4".  :|

Benno