Subject: draft-ietf-conneg-media-features-02.txt

From: Graham Klyne <[email-masked]>
Date: Mon, 16 Nov 1998 17:45:07 +0000

Another round of review, based on my experiences with fax-schema, etc.

>draft-ietf-conneg-media-features-02.txt
>Media Features for Display, Print, and Fax

[...]
>1. Introduction
>    
>   Media features may be used in many different protocol situations.
>   Those defined in this specification can indicate the display or
>   printer dimensions (in pixels), color capability and bit-depth, or
.........................................................^^^^^^^^^

I assume this will get pulled wen the new color= tag is introduced.

>   media type.  The physical dimensions of a display can be inferred
>   from the display size and display resolution. In the case of paper
>   output, the paper size may be expressed as a token from a list of
>   standard paper sizes.  These are presented formally in the
>   Notation section.

[...]
>2.1 Image Size
>
>   - Media Feature tag name(s): 
>
>     pix-x
>     pix-y
>    
>   - ASN.1 identifier associated with this feature tag:
>
>     ***New assignments by IANA***
>
>   - Summary of the media features indicated by this feature tag:
>
>     These features indicate the display size of the recipient for
>     display or print, measured in pixels; they indicate horizontal
>     (pix-x) and vertical (pix-y) dimensions.
>
>   - Values appropriate for use with this feature tag:
>
>     Signed Integer

Since all Integers are 'signed' in [REG], how about:

#     Integer (>0)

?

[...]
>2.2 Resolution
>     
>   - Media Feature tag name: 
>   
>     dpi
>     
>   - ASN.1 identifier associated with this feature tag:
>   
>     ***New assignments by IANA***
>
>   - Summary of the media features indicated by this feature tag:
>
>     This feature indicates the resolution that the recipient can
>     display or print without loss, measured in pixels per inch.
>     Typically resolution capability is represented as dots-per-inch
>     rather than in SI units [SI]. Values for dpi may be expressed as
>     a rational to accomodate resolution of SI-based devices; for
>     example dpi=19558/100 can be used to represent a resolution of 77
>     dots per centimeter.
>  
>   - Values appropriate for use with this feature tag:
>
>     Rational

#     Rational (>0)

[...]
>2.3 Registration of 'media'
>   - Media Feature tag name(s):
>     
>     ua-media
>
>   - ASN.1 identifier associated with this feature tag:
>   
>     ***New assignments by IANA***
>
>   - Summary of the media features indicated by this feature tag:
>     
>     This feature indicates the recipients device media, indicated
>     with an simple token.
>
>   - Values appropriate for use with this feature tag:
>     
>     Token with an equality relationship. Typical values include:

QUESTION:  do we want "typical values include", or "legal values are" with
scope for registration of additional legal values?

The disadvantage I see with the former is that it leaves a possibility for
different applications to use different feature values with the same
meaning, hence potentially defeating content negotiation goals.

>     screen           A refreshable display
>     screen-paged     a refreshable display which cannot scroll 
>     stationery       Separately cut sheets of an opaque material
>     transparency     Separately cut sheets of a transparent material
>     envelope         Envelopes that can be used for conventional
>                      mailing purposes
>     envelope-plain   Envelopes that are not preprinted and have no
>                      windows
>     continuous       Continuously connected sheets of an opaque
>                      material

Reference to source where these are defined? 

>2.4 Paper Size
>     
>   - Media Feature tag name(s):
>     
>     paper-size
>     
>   - ASN.1 identifier associated with this feature tag:
>     
>     ***New assignment by IANA***
>     
>   - Summary of the media features indicated by this feature tag:
>     
>     For stationery, it is often useful to have information about the
>     size of display used.  While it is more precise and predictable
>     to use absolute resolution and pixel sizes, some applications
>     find it useful to provide paper size in addition to this
>     information. Note that not all of the paper may have a printable
>     area.

I suggest:

#     For stationery, it is often useful to have information about the
#     physical size of the stationery used (e.g. for incorporation into
#     a folder of printed materials).  This may affect the choice or
#     formatting of data used, but rendered size information is conveyed
#     primarily by other feature tags.
#
#     Note that not all of the paper may have a printable area.
     
>   - Values appropriate for use with this feature tag:
>     String with equality

Is that 'string' or 'token'?

Was there a question raised that these are not the same as those used
elsewhere (printer MIB?)?

>     letter:        8.5x11.0 inches 
>     A4:            210x297 mm    
>     B4:            250x353 mm
>     A3:            297x420 mm            
>     legal:         8.5x14 inches

[...]
>2.5 Color and greyscale     
>   - Media Feature tag name(s):

To be replaced (I assume).

>   paper-size=iso-a4
>      indicates the display size is 210x297mm. 

Mismatch with description given above.

#g

------------
Graham Klyne
([email-masked])