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Subject: image scale-to-fit in DITA 1.2

Since we were (trying to) keep DITA 1.1 minimal so that we could
get it out sooner, we passed on adding a scale-to-fit capability
to DITA graphics (the image element).

Our customers are needing such a capability--to the point that we
will probably have to provide it in a non-standard way for the time
being--so I'd like to see it considered for DITA 1.2.

Background (can be skipped)
Graphic sizing is always complex and generally misunderstood.  HTML
(and CSS's) (mis-)handling only exacerbates the issue.  XSL-FO has 
the full range, but in a way that requires attributes with odd data
types (e.g., sizes, percentages, and enumerated values all in one

One relatively complete (but not necessarily the clearest) discussion
is one related to DocBook (but built on CALS concepts) at
(Note that DITA's width and height attributes correspond to DocBook's
width and depth attributes [and CALS' reprowid and reprodep attributes];
DITA has no attributes corresponding to DocBook's contentwidth and
contentdepth as described in the above referenced web page.)

I wrote about graphic sizing previously at

DITA 1.2 Enhancement request
The current user requirement is to allow a user to request 
that an image be scaled to fit within the "available space".

The simplest way to accomplish this given what we have to date is to
add a "scalefit" attribute properly defined.  This matches what CALS
has done for decades and is a subset of what the latest DocBook does.

Adding the scalefit attribute, the sizing attributes for image would be:

<ATTLIST image
      . . .
      height     NMTOKEN                          #IMPLIED
      width      NMTOKEN                          #IMPLIED
      scale      NMTOKEN                          #IMPLIED
      scalefit  (yes | no | 
                        -dita-use-conref-target)  #IMPLIED

If, for a given image, any one of height, width, or scale is specified,
those attributes determine the graphic size (as is already the case
in DITA 1.1), and any setting of scalefit would be ignored.  If none
of those attributes are specified and scalefit="yes", then the image 
would be scaled (the same factor in both dimensions) so that the 
graphic would just fit within the available height or width (whichever 
is more constraining).  

The available width would be the prevailing column (or table cell) 
width--that is, the width a paragraph of text would have if the graphic 
were a paragraph instead.  The available height is implementation
dependent, but if feasible, it is suggested to be the page (or table 
cell) height or some other reasonable value. 


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