Structure vs. Value and Contradictory Criteria

It might not be possible to avoid all conflict, but whenever possible
guidelines and criteria should address access to language structures and
parameter values rather than prescription of specific values.

Since this is abstract let me be specific.  Languages that can be read by
machines like HTML with CSS, PDF, Flash and Silverlight have one thing in
common. They have structures that can be determined programmatically,
otherwise machines could not read them.  The structures that can be
determined programmatically can be changed with 100% accuracy. Other
structures cannot.

Example: Tags for lists in PDF along with their meaning to the content can
be determined programmatically. The "class" attribute in is assigned a
string by the programmer, but a program cannot determine its meaning within
the context of the an HTML document. The CSS parameter "color" is given a
value that totally determines its meaning within the content. The "span"
element has non-deterministic meaning.

WCAG should always insist that items that can be exposed deterministically
are exposed that way. This will enable change to structures and values
required for flexibility.

Example: Overriding the authors color choices. if color is primarily
determined by foreground and background color attributes values choices
these can be changed. Problems with other non-deterministic formats.  A
programmer may hide text by making text the same color as background. If
you change the colors you make something visible that should not be. This
should be a prohibited configuration. It is like using an H1 because you
like the font size. A programmer may use a background image. How does an AT
modify the foreground color.   You cannot determine the background color
programmatically. Is there a deterministic way to do this or how can we
change this?

Increasing the determinism of content seems to be a way to expand WCAG
without creating conflicts.

Wayne