HTML tags – specific instructions understood by a web browser or screen reader. One type of HTML tag, called an “alt” tag (short for “alternative text”), is used to provide brief text descriptions of images that screen readers can understand and speak. Another type of HTML tag, called a “longdesc” tag (short for “long description”), is used to provide long text descriptions that can be spoken by screen readers.
Upon discovering issues faced by disabled government employees and the public, revisions to section 508 were made. The issues that were uncovered involved websites, documents, and software programs. As of January 2018, the updated 508 standards require all federal agencies and contractors to create web content accessible to all. The updated standards also include Website 508 compliance.
The type of operating system and hosting doesn’t matter much for design, but the platform is a factor. For instance, if you need a WordPress theme, the designer must work with WordPress themes and customize them in a way that a developer can feasibly code in CSS or JavaScript on the front end. If you use another CMS, the developer must work with those elements. Most designers specialize in specific platforms, so review their portfolios and experience for specific platforms before you invite them to bid on your project.
The U.S. Department of Transportation enforces regulations governing transit, which includes ensuring that recipients of federal aid and state and local entities responsible for roadways and pedestrian facilities do not discriminate on the basis of disability in highway transportation programs or activities. The department also issues guidance to transit agencies on how to comply with the ADA to ensure that public transit vehicles and facilities are accessible.

Error prevention on important forms (3.3.4): For pages that create legal commitments or financial transactions or any other important data submissions, one of the following is true: 1) submissions are reversible, 2) the user has an opportunity to correct errors, and 3) confirmation is available that allows an opportunity to review and correct before submission.
The Supreme Court decided under Title II of the ADA that mental illness is a form of disability and therefore covered under the ADA, and that unjustified institutional isolation of a person with a disability is a form of discrimination because it "...perpetuates unwarranted assumptions that persons so isolated are incapable or unworthy of participating in community life." The court added, "Confinement in an institution severely diminishes the everyday life activities of individuals, including family relations, social contacts, work options, economic independence, educational advancement, and cultural enrichment."

This title is designed to help people with disabilities access the same employment opportunities and benefits available to people without disabilities. Employers must provide reasonable accommodations to qualified applicants or employees. A reasonable accommodation is any modification or adjustment to a job or the work environment that will enable an applicant or employee with a disability to participate in the application process or to perform essential job functions.  

Mention ADA compliance to many web developers and you may encounter a blank stare. First, find an agency working with the web platform or framework you use and ask about how their development workflow addresses accessibility. Most platforms have a partner directory. From there, you can start vetting agencies for their actual experience with web accessibility.
Case law has been the most helpful in illuminating the implications of the ADA for websites.There have been lawsuits involving companies like Expedia,, Southwest Airlines, and Target as defendants and primarily featuring accessibility organizations as plaintiffs. These cases had mixed results, but each helped clarify the ADA's jurisdiction on the web. 
Hey OB – Disclaimer – none of this is legal advice and you’d want to check with a lawyer to know if you’re at risk for any action if you’re not ADA compliant. Based on what we’ve seen if you don’t have a physical retail or service location, and you don’t receive any funding from the government you likely aren’t required to have a website that would be considered compliant. Some people expect that to change in the next few years, but that’s what we know for now. Let us know if you have more questions or would like to test your site.
In the context of employment, the ADA prohibits employers from taking disability into consideration in all aspects of the employment relationship—from hiring to firing and virtually everything in between. The law also requires employers to make reasonable accommodations for individuals with disabilities to help them do their job. Outside of employment, the ADA requires most public places, such as shops, restaurants, and movie theaters, to be accessible to those with disabilities. State and local laws can also provide further protections.

The Department has assembled an official online version of the 2010 Standards to bring together the information in one easy-to-access location.  It provides the scoping and technical requirements for new construction and alterations resulting from the adoption of revised 2010 Standards in the final rules for Title II (28 CFR part 35) and Title III (28 CFR part 36).