strings joined with " " (Space), while RFC says they must be joined without adding space.
As defined in [RFC1035], Sections 3.3 and 3.3.14, a single text DNS
record can be composed of more than one string. If a published
record contains multiple character-strings, then the record MUST be
treated as if those strings are concatenated together without adding
spaces.
https://github.com/zaccone/spf/blob/master/spf.go#L109
strings joined with " " (Space), while RFC says they must be joined without adding space.
https://tools.ietf.org/html/rfc7208#section-3.3