As per RFC4408 3.1.3, a TXT record can be split up with quotation marks and will be reassembled properly - this is a way of getting around the 255 character limit on record size.
IN TXT "v=spf1 .... first" "second string..."
MUST be treated as equivalent to
IN TXT "v=spf1 .... firstsecond string..."
If a record has 3 or more parts, what determines the order in which the records are concatenated?