Subject: I-D ACTION:draft-lundblade-1pass-mult-alt-00.txt

From: [email-masked]
Date: Mon, 10 Nov 1997 10:45:52 -0500

A New Internet-Draft is available from the on-line Internet-Drafts directories.

	Title		: One Pass Multipart/Alternative Processing
	Author(s)	: L. Lundblade
	Filename	: draft-lundblade-1pass-mult-alt-00.txt
	Pages		: 4
	Date		: 07-Nov-97
	
Most MIME syntax and semantics can usually be processed in a single
pass through the data.  For example, the MIME boundary parameter always
appears before it is used.  Similarly the security multiparts
explicitly list the hash algorithm before the hashed (signed) data so
the correct hash algorithm can be used to calculate the hash on the
data as it is processed.
 
This is not the case with multipart/alternative MIME structures.  The
processor of the data cannot know the MIME types of the altnernatives
present until all alternatives have been processed. Thus, it is not
possible for a one pass processor to consider more than the first and
most limited representation, because the second part or subsequent may
be something that cannot be handled.
 
A particular case of this occurs with alternative representations of
types text/plain and text/html or text/enriched formats.  The
text/plain representation must come first as required by the
multipart/alternative standard.  If the processing is being done on a
small device with limited memory it is most desirable to process the
structure in one pass.  If the display is also small, for example 40
colums rather than 80, it is desirable to use the text/html alternative
because it appropriate to reflow HTML to fit the display.  Essentially,
given some text that was composed with more than plain markup, (e.g.,
HTML), it is preferrable to format the text with knowledge of the
display, than use generically formatted text (i.e., the text/plain
part).
 
This memo proposes a parameter addition to the multipart/alternative
MIME type that lists the MIME types of its alternative components.
This allows a one-pass processor of the multipart/alternative entity to
pick which alternative to use before processing the entire entity.

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