ADA American Disabilities Act
No one should be discriminated against owing to his/her disability regarding the complete and equivalent access to and enjoyment of all services, goods, advantages, privileges, facilities, or accommodations of any location of “public accommodation”.
How much this applies to Web sites, is still being worked out in the courts.
Different courts across America have stated that commercial websites can be considered as a place of public accommodation, therefore, they can be subjected to the ADA guidelines.
In other cases, it is stated that websites can be subjected to ADA regulations if there is a close connection between the site and a physical location. 
There are certain courts that have even concluded that the ADA in its simple written form simply does not grant any form of protection for any online user. 
WHAT’S A PROGRAMMER TO DO?
The same folks who brought you the Internet have developed standards. The Web Content Accessibility Guidelines (WCAG) international standard, includes WCAG 2.0, WCAG 2.1, and WCAG 2.2. WCAG documents explain how to make web content more accessible to people with disabilities.
The WCAG standards have 12-13 guidelines. The guidelines are organized under 4 principles: perceivable, operable, understandable, and robust.
For each guideline, there are testable success criteria. The success criteria are at three levels: A, AA, and AAA.
Level A issues are the more urgent, including problems that can greatly limit a disabled user’s ability to navigate or use the website. 
Level AA issues incline towards functionality, with focus on areas where improvement is required to give disabled users the complete experience of a website. (Level AA is deemed as the target standard for several commercial websites.)
The highest standard is Level AAA issues, fine-tuning and expanding on issues recognized as Level A and AA. While it is a good goal, complete Level AAA compliance tend to be beyond the grasp of most websites.
So, if you get slapped with a lawsuit, adhering to WCAG standards may help you in court.

Some of the challenges:
Nevertheless, there are certain items that are much more difficult to fix depending on the circumstance. Such include the following:
Your site should be completely navigable through keyboard only. This usually involves things like skip navigation buttons and can include manually setting a tab index everywhere.
Text should meet a minimum contrast ratio against the background, which can greatly affect your design.
Your site should handle text scaling up to 200% without creating any horizontal scrolling or content-breaking layout issues. This may be more challenging to fix in some quite complex designs.
Your site should be navigable with any screen reader software. This can be challenging to test and can include some grueling fixes just as what is required for keyboard navigation.
Why should we care?
If you ignore website accessibility, you are not only failing your civic responsibility, you are likely also missing out on getting new customers. The 2010 census reports that 19% of the US population, roughly 56.7 million people, have a form of disability or the other.  Do you really want to ignore one potential customer out of five?
Do you want to lose business from government and other organizations that care about web pages being accessible?
Mostly from: https://bmmagazine.co.uk/business/website-ada-compliance-what-it-is-how-it-works-and-why-you-need-to-do-it/
With some details from: https://www.w3.org/WAI/standards-guidelines/wcag/
There are tools to test web sites for accessibility.
WAVE, by WebAIM, is one of the most popular web accessibility testing tools in the market 
Using the web service, a user needs only to enter the URL they want tested into the form on https://wave.webaim.org/
Unfortunately, some Web Overlay producers have products that interfere with disability testing.
https://overlayfalseclaims.com/anti-competitive-behavior.html

Disability Lab
Check out https://wave.webaim.org/ the disability tester for Web pages.
Run it on itself.  (It gives itself high marks.)
Run it on a web page you use.  What do you find?
At the end of the semester, run it on your project. How accessible is your project web page?
Check out what is available at a company like https://www.freedomscientific.com/
(which markets JAWS)
What issues do you see as important for a web designer who wishes the web page to be accessible?
(Short essay)

The visually impaired
Initially, visually impaired people had a difficult time using computers.
But some pioneers were determined.  One mechanical engineer, after he was blinded in an accident, hired a high school student to read programming books, which he taped.  He would type code, and have someone read the screen back to him.
In 1987, a firm he helped found produced a screen reader for DOS. It was not the first screen reader, but it had features that other did not. In the winter of 1995, they released a version for Windows. That software still has a huge market share.
In 2020, around 50 million people around the world were blind.  Another 250 million had visual impairments.  And, in a survey of software developers, 1.7% of them checked the box “I am blind / have difficulty seeing.”
Do you really want to exclude that many people?
Mostly from https://www.theverge.com/23203911/screen-readers-history-blind-henter-curran-teh-nvda
Personal note: As an undergraduate, I participated in a programming contest.  One of the judges was both blind and deaf.  He communicated by reading braille.  I was a volunteer who kept him up to date on events.  I typed, it came out in Braille for him. He typed,  it came out on a screen for me.
The programming contest could not have happened without that judge.

Even with screen readers, visually impaired people find it very difficult to handle things like charts.
Amazingly some researchers actually created a Javascript file that allows the visually impaired to interact with charts.  It has been made available as a free service.
1.	Ather Sharif, Olivia H. Wang, Alida T. Muongchan, Katharina Reinecke, Jacob O. Wobbrock. VoxLens: Making Online Data Visualizations Accessible with an Interactive JavaScript Plug-In. CHI 2022 (Project presented), 2022 [abstract]
Cited in
University of Washington. "VoxLens: Adding one line of code can make some interactive visualizations accessible to screen-reader users." ScienceDaily. ScienceDaily, 1 June 2022. <www.sciencedaily.com/releases/2022/06/220601155513.htm>.