RE: Alternative Formats

>  . . . I was referring to all formats, such as visual, audio, and 
written. I do see where all 3 
> of these would fall into web accessibility. Visual for graphics, audio 
for sound, and 
 > written for downloading files as PDF or TXT. Do you agree? 

Well, I would expand your simple list to also include the following, 
quoted from Understand WCAG:

Controls, Input: If non-text content is a control or accepts user input, 
then it has a name that describes its purpose. (Refer to Guideline 4.1 for 
additional requirements for controls and content that accepts user input.) 

Time-Based Media: If non-text content is time-based media, then text 
alternatives at least provide descriptive identification of the non-text 
content. (Refer to Guideline 1.2 for additional requirements for media.) 
Test: If non-text content is a test or exercise that must be presented in 
non-text format, then text alternatives at least provide descriptive 
identification of the non-text content. 
Sensory: If non-text content is primarily intended to create a specific 
sensory experience, then text alternatives at least provide descriptive 
identification of the non-text content. 
CAPTCHA: If the purpose non-text content is to confirm that content is 
being accessed by a person rather than a computer, then text alternatives 
that identify and describe the purpose of the non-text content are 
provided, and alternative forms of CAPTCHA using output modes for 
different types of sensory perception are provided to accommodate 
different disabilities.
Decoration, Formatting, Invisible: If non-text content is pure decoration, 
is used only for visual formatting, or is not presented to users, then it 
is implemented in a way that it can be ignored by assistive technology.

Regards,
Phill Jenkins
IBM Research - Human Ability & Accessibility Center
http://www.ibm.com/able