While reading output, more than 2000 bytes can force
earlier bytes to be "forgotten". This may be
changed with the function match_max. (Note that
excessively large values can slow down the pattern
matcher.) If patlist is full_buffer, the corre-
sponding body is executed if match_max bytes have
been received and no other patterns have matched.
Whether or not the full_buffer keyword is used, the
forgotten characters are written to
expect_out(buffer).