There are three forms of whitespace:
o WSP represents simple whitespace, i.e., a space or a tab character (formal definition in [RFC5234]).
o LWSP is linear whitespace, defined as WSP plus CRLF (formal definition in [RFC5234]).
o FWS is folding whitespace. It allows multiple lines separated by CRLF followed by at least one whitespace, to be joined.
The formal ABNF for these are (WSP and LWSP are given for information only):
WSP = SP / HTAB LWSP = *(WSP / CRLF WSP) FWS = [WSP CRLF] 1WSP
The definition of FWS is identical to that in [RFC5322] except for the exclusion of obs-FWS.
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