SC 1.3.5: meaning-critical sequences

The concept that this phrase is trying to communicate is that there is
some content for which the order of the content is critical to correctly
understanding its meaning. For other content, it is not critical. This
is true at different levels of granularity, so that the order within
some portion of the content is critical, but the larger units of content
can be reordered without affecting meaning.

For example, you should be able to change the order of items in an
unordered list without affecting its meaning. But not of an ordered
list. So an ordered list marks a meaning-critical sequence, but an
unordered list does not. 

Text in a container (paragraph, list item, table cell, etc) is always a
meaning-critical sequence. Tables are meaning-critical sequences. The
paragraphs in an article are a meaning-critical sequence. The ordering
of a navigation bar and a search tool, however, is not meaning-critical.

If contents contain images, is there location meaning critical? There
are usually (but not always) a number of different places the image
could occur in the content without affecting the meaning.

For those of you who are more knowledgeable about html and css, how do
you know when it is safe to relocate an element in css, and when it is
not?

(In describing this, I realize that "meaning-critical sequences" is not
a good phrase to be using. It makes it sounds as if some sequences or
sections of content are critical to meaning, and other sequences or
sections of content are not.)

In order to understand the content, especially when preparing alternate
presentations, 
1.	We need to be able to programmatically determine when the
alternate presentation can safely change the order of the content. (I
believe the default for most content in most technologies is that the
order cannot be changed.)
2.	Where the programmatically determined order of the content can't
be changed, we need it to be a meaningful order.

The second requirement can really only be checked manually, much like
checking whether an alternate description is equivalent to its image.

Does this explanation make sense? Does anyone have ideas of alternate
wordings for the techniques and/or success criterion that would make it
less confusing?

Loretta Guarino Reid
lguarino@adobe.com
Adobe Systems, Acrobat Engineering