Implementing details for 3.1.2 (Configurable Default Rendering)

This includes minor copy editing of the SC.

3.1.2 Configurable Default Rendering: The user has a global option to 
specify which types of alternative to render by default and, in cases 
where the alternative content has different dimensions than the original 
content, how the layout/reflow of the document should be handled. (Level A)

    * Intent of Success Criterion 3.1.2:

When the author provided alternative content, it is wasted if the user 
agent doesn't render it for users who need it. This is a global option 
because it would be an unreasonable burden for the user to have to 
change the rendering options every time they visit a new page.

    * Examples of Success Criterion 3.1.2:

          o In the browser's preferences dialog box, a user specifies 
that they want Alt text displayed in place of images, and that the 
document should reflow to allow the entire Alt text to be displayed 
rather than truncated.

          o In the browser's preferences dialog box, a user chooses to 
always display the alternative ("fallback") content for embedded 
objects, such as videos.

          o The user toggles a menu item which turns on the display of 
all captions for video and audio content.

    * Related Resources for Success Criterion 3.1.2:

          o To be written

(From Jim and Greg)