[Fontinst] On the proper look of the \AA

[Vladimir Volovich]

The following message is a courtesy copy of an article
that has been posted to comp.text.tex as well.

Greetings,

there have been some discussion on the CyrTeX-ru mailing list about
the proper appearance of the glyphs representing the ANGSTROM SIGN
(U+212B) and the LATIN CAPITAL LETTER A WITH RING ABOVE (U+00C5).

When the font encoding contains the pre-built glyph(s) angstrom and
Aring, there is basically no question - the decision on the proper
look of these glyphs is under font designer's control. However, when
the font encoding doesn't contain the pre-built glyph, TeX can
construct it using the glyphs for LATIN CAPITAL LETTER A and the RING
ACCENT which are often available.

For example, the T1 font encoding contains Aring; but OT1 font
encoding doesn't; so TeX can construct this glyph from A and ring.

It is possible to just apply the ring accent to the letter A using the
\accent command; but for some reason Donald Knuth decided to make the
special command \AA to generate the Aring, which puts the ring accent
close to the letter A (without a gap). Similar approach is used in
LaTeX, which defines a \DeclareTextCompositeCommand for the
combination "\r A" in ot1enc.def and ot4enc.def.

Note that Jorg Knappen's EC fonts (T1 encoding) which contain the
pre-built Aring glyph, put the ring close to A (without the gap), so
the Aring looks exactly the same as \AA when constructed artificially
when using the OT1 font encoding (CM fonts).

I noticed that not only CM fonts use "gap-less" Aring, -- various other
fonts (not TeX-related) contain "gap-less" Aring; while some other
fonts treat Aring as A with the ring accent, and put the ring just
like other accents.

To see the difference of both variants, you can process this LaTeX file:

\documentclass{article}
\usepackage[T1]{fontenc}
\begin{document}

\AA % default appearance
% undefine the special \r{A} composite definition:
\expandafter\let\csname \string\T1\string\r-A\endcsname\relax
\AA % using just \accent

\end{document}

Some arguments for the special look of Aring (which I share):

1) D.Knuth defined a special command for \AA, which puts ring close to
   A instead of using \accent

2) the same approach is used in LaTeX in ot1enc.def and ot4enc.def,
   and LaTeX has in mind not only the CM fonts, but any font families,
   so these definitions are meant to be applied not only to CM fonts.

3) The fontinst package contains some code to put the ring close to A
   (the glyph ringfitted defined in latin.mtx, and used in ot1.etx).
   (and this package is meant to be used for installation of "arbitrary"
   fonts)

4) the article http://en.wikipedia.org/wiki/%C5 in the Online
   Encyclopedia states that:

  The letter "\r{A}" is often perceived as an "A" with a ring,
  interpreting the ring as a diacritic mark. However, the ring is not a
  diacritic. Rather, the letter developed as a form of semi-ligature of
  two consecutive "A"s.

   so this gives some basis to think that ring might be located not as
   plain accent, but closer to A.

5) my memories about the look of the Angstrom sign in the books
   suggest that it should be written as plain TeX does it.

Arguments against the close placement of the ring (from Alexander
Lebedev and Lars Engebretsen) state that from aesthetic reasons the
ring should be put on the same height as other accents. E.g., the
Bitstream specification for developers of new fonts contains an
example of Aring on page 5 and an example of accents on page 4:
http://www.bitstream.com/categories/products/nfc/NFCSubmissions.pdf

I have some questions to experts:

1) what was the rationale to use the special definition of \AA - why
   not just use the \accent to put the ring over A?

2) is this rationale only a design decision of the Computer Modern
   fonts, or it can be applied to other font families? I.e., shall the
   ring in the Aring glyph be put with a gap of the same widths as all
   other accents, or it is preferred to use "gap-less" Aring?

3) should the glyphs for the LATIN CAPITAL LETTER A WITH RING ABOVE
   and the ANGSTROM SIGN be the same in respect of the placement of
   the ring above A? (I.e., maybe the ring over A in U+00C5 should be
   put as an accent; but the preferred placement of the ring over A in
   the angstrom sign U+212B is without the gap).

Many thanks in advance for your comments.

Best,
v.