\
’
e
”.
The TeX output stream is in a somewhat different situation:
characters in it are to be used to select glyphs from the fonts to be
used. Thus the encoding of the output stream is notionally a font
encoding (though the font in question may be a
virtual font). In principle, a
fair bit of what appears in the output stream could be direct
transcription of what arrived in the input, but the output stream
also contains the product of commands in the input, and translations
of the input such as ligatures like
fi
.
Font encodings became a hot topic when the
Cork encoding
appeared, because of the possibility of suppressing
\
accent
commands in the output stream (and hence improving the
quality of the hyphenation of text in inflected languages, which is
interrupted by the \
accent
commands — see
“how does hyphenation work”).
To take advantage of the diacriticised characters represented in the
fonts, it is necessary to arrange that whenever the
command sequence “\
’
e
” has been input
(explicitly, or implicitly via the sort of mapping of input mentioned
above), the character that codes the position of the “é” glyph is
used.
Thus we could have the odd arrangement that the diacriticised character in
the TeX input stream is translated into TeX commands that would
generate something looking like the input character; this sequence of
TeX commands is then translated back again into a single
diacriticised glyph as the output is created. This is in fact
precisely what the LaTeX packages inputenc and
fontenc do, if operated in tandem on (most) characters in
the ISO Latin-1 input encoding and the T1 font encoding.
At first sight, it seems eccentric to have the first package do a thing, and
the second precisely undo it, but it doesn’t always happen that way:
most font encodings can’t match the corresponding input encoding
nearly so well, and the two packages provide the sort of symmetry the
LaTeX system needs.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=whatenc