Bruce Lilly writes:
Display (as opposed to generation) does not require information about
header field syntax
False. See RFC 2047, section 6.1. Encoded words can appear as
* substrings (up to 75 bytes) of fields defined as unstructured,
* words inside phrases in fields defined as structured, and
* substrings of comments in fields defined as structured.
This is, as I said, an extremely complicated set of locations. Even
worse, as I said, it is an unstable set of locations.
RFC 2047 explicitly provides for considering
unrecognized fields as unstructured *for the purpose of display*.
False. You are confusing extension fields with user-defined fields; see
RFC 822. Every structured extension field changes the set of locations
where RFC 2047 encoded words can appear.
---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago