> I guess we're talking about U+00A7, the section sign, \S in
> plain.tex?
Yes, and \P. Note, however, that both @S and @P work within a texinfo
document. It's just that texinfo.tex's \DeclareUnicodeCharacter for
`§' and `¶' (which use `\S' and `\P' for its definition) seem to be
modified, resulting in an undefined control sequence (not undefined
glyph), while other characters like `†' or `‡' are displayed
correctly.
BTW, I forgot to mention the used versions.
`texinfo.tex 2015-12-20.12' from the texinfo repository, and
`luatex beta-0.80.0 (TeX Live 2015) (rev 5238)' and all other input
files as provided by the TeXLive tree at rev 39201.
Werner
