`--buf-size=n`

  Set the the maximum number of characters simultaneously present in current lines of open files and in control sequences between \csname and \endcsname. &TeX; uses the buffer to contain input lines, but macro expansion works by writing material into the buffer and reparsing the line. As a consequence, certain constructs require the buffer to be very large, even though most documents can be handled with a small value.

  --buf-size=n