除非转义令牌，但忽略转义的转义符，否则在令牌上拆分字符串

I'm trying to use regular expressions to split an EDIFACT line. In EDIFACT, the components of a line are separated by a token, usually "+". The "+" can be escaped by preceding it with a "?". I can achieve this much using the expression I'm trying to use regular expressions to split