[Accessibility-handlers] magnification use case

Neil Soiffer neils at dessci.com
Mon Aug 6 10:33:21 PDT 2007

Here's my contribution for magnification.  I started to put this on the
group's Wiki page, but couldn't figure out how to create a new page.
Gregory, can you help me out on putting this up on the Wiki?
Magnification use cases:
The most obvious use of magnification is for rendering the entire
content larger.  For text-based (or more generally, font-based)
applications, this means that AT software should be able to request
rendering with larger sized fonts or a certain amount of magnification
relative to some baseline magnification.  Applications beyond standard
text-based ones include math, music, and labeled plots/graphics.  For
non text-based applications such as graphics and chemical structures,
magnification could be based on a certain percentage of the normal size
or given by "fill this area".  I believe these two ideas can always be
mapped onto each other.  In all of these cases, the magnification may be
due to having the entire documented magnified or it may be due to a
request to magnify an individual instance (such as an equation).
There are two other uses for magnification:
1.  While navigating or speaking, it might be desirable to magnify the
part being navigated/spoken to make it easier to see.  Eg, while playing
some music, the current measure and next measure might be magnified to
ease reading while leaving the rest unmagnified so that the amount of
screen space used is minimized.  There would also need to be a method to
reset the magnification.
2.  Math and Chemical notation shrink fonts for superscripts and
subscripts.  In math, these are further reduced for nested scripts.  On
common feature for math renderers is to set a minimum font size.
Typically, this is 50% of the base font size and corresponds to the size
used for doubly nested scripts.  It is potentially useful to allow the
AT to control the maximum percent shrinkage used by renderers.  Another
possibility is to have a feature that says "don't shrink at all".
Although the rendering would not be consider high quality typesetting,
it does make scripts more readable to those with some vision impairment.
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