web2c: \input quoted filename
4.5.1 '\input' quoted filename: '\input "some name"'
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As of Web2c version 7.5.3 (2004), double-quote characters can be used to
include spaces or other special characters. In typical use, the '"'
characters surround the entire filename:
\input "filename with spaces"
Technically, the quote characters can be used inside the name, and
can enclose any characters, as in:
\input filename" "with" "spaces
One more point. In LaTeX, the quotes are needed inside the braces of
its '\input' macro, thus:
\input{a b} % fails
\input{"a b"} % ok
There is no way to quote the quote character.