What does a "heavily extended" or "enhanced" font mean?

Question

I was looking at fonts and I came up with TeX Gyre Schola. Then I saw on its entry on The LaTeX Font Catalogue:

The TeX Gyre Schola family of fonts is based on the New Century Schoolbook family, but heavily extended.

When looking at the New Century Schoolbok entry, I got the following:

An enhanced version is available with the TeX Gyre Schola font.

So, my question is: What makes a font the "enhanced" or "extended" version of another one? What do they usually mean with this adjectives?

Answer 1

TeX Gyre Schola (TGS) is based on Century Schoolbook, rather than New Century Schoolbook (NCS); this is confirmed by the choice of the family names, made according to Karl Berry's font naming scheme: it is cs for the former and nc for the latter. However this is unimportant, because the basic letter shapes are exactly the same for both:

\documentclass{article}
\newcommand{\alphabet}{%
  ABCDEFGHIJKLMNOPQRSTUVWXYZ\\
  abcdefghijklmnopqrstuvwxyz}

\setlength{\parindent}{0pt}

\begin{document}
\fontfamily{pnc}\selectfont
New Century Schoolbook\\
\alphabet

\medskip

\fontfamily{qcs}\selectfont
\TeX\ Gyre Schola\\
\alphabet

\end{document}

Indeed, the design of TGS is based on the URW clone of NCS, precisely Century Schoolbook L.

Where the main differences are is in the output encodings available with TGS:

• T1 (Cork encoding for European languages)
• TS1 (text companion font
• T5 (Vietnamese)
• OT1 (Knuth TeX encoding)
• OT4 (old encoding for Polish)
• LY1 (Western Europe language, with more ligatures, but no Eastern diacritics)
• L7X (Lithuanian)
• IL2 (Czech and Slovak)
• QX (Polish)

NCS is only available in the T1, TS1, T5 and OT1 encodings. It also has the OMS and OML math encodings, used by the fouriernc package. The glyph coverage of the TS1 encoding is complete with TGS, while only a few glyphs are present in NCS. The glyphs for “perthousandzero”, "dotless j", "Eng" and "eng” are missing in the T1 encoding for NCS.

There are also other enhancements. TGS has upright, italic, small caps and italic small caps both in medium and boldface series. The small caps fonts are “true”, while those available with NCS are “faked” by resizing uppercase letters.

There is no small caps italic for NCS.

Finally, TeX Gyre Schola is available also as an OpenType font, while for New Century Schoolbook there is no such format in the free TeX distributions and one must rely on it to be supplied by the operating system or buy it.