When an operand failed to parse, the content parser went back to the
byte after its start and tried again, so a run of n bytes that never
reads as a number (a long run of '+', or digits ending in a letter) was
read again from every one of its bytes: n^2/2 bytes from a tiny
compressed stream. A failed number token longer than 64 bytes is now
skipped whole; shorter ones still recover byte by byte.