This is a huge topic that I can only cover at a fairly basic level in this site. There are key concepts and relatively simple rules that everyone who creates online material needs to follow, which is the focus of this site. I include links to more advanced information when I find it, but my emphasis is on what we can all do to create online materials to be accessible to most users.
As you design web-based materials, you need to consider many, many things. There are legal reasons for creating materials to be accessible, but there are also practical reasons - you want your visitors to be able to use your site!
The following are from the Glossary on the Accessible Web Design site (https://www.joedolson.com/glossary.php)
Web Accessibility
The principle that all web users should have access to information available on the internet.
Web Accessibility Initiative
A body from the World Wide Web Consortium dedicated to discussing and setting standards for web accessibility.
World Wide Web Consortium (W3C)
The World Wide Web Consortium is a non-profit organization founded by Tim Berners-Lee which is responsible for setting the standards for common web creation and access methods. Major documents include the specifications for the HTML and XHTML languages and the Web Content Accessibility Guidelines.
Web Content Accessibility Guidelines (WCAG)
The Web Content Accessibility Guidelines are a set of guidelines intended to help web content authors prepare their content for use by people with disabilities.
There are many checklists and indexes sites use to help organize their information. If you scan over just a few of these lists, you will see a pattern to the types of things you want to learn more about.
WCAG 2.0 Quick Reference List (http://www.w3.org/WAI/WCAG20/quickref/) :
1.1 Text Alternatives: Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language.
1.2 Time-based Media: Provide alternatives for time-based media.
1.3 Adaptable: Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
1.4 Distinguishable: Make it easier for users to see and hear content including separating foreground from background.
2.1 Keyboard Accessible: Make all functionality available from a keyboard.
2.2 Enough Time: Provide users enough time to read and use content.
2.3 Seizures: Do not design content in a way that is known to cause seizures.
2.4 Navigable: Provide ways to help users navigate, find content, and determine where they are.
3.1 Readable: Make text content readable and understandable.
3.2 Predictable: Make Web pages appear and operate in predictable ways.
3.3 Input Assistance: Help users avoid and correct mistakes.
4.1 Compatible: Maximize compatibility with current and future user agents, including assistive technologies.
Accessibility: WCAG2 at a Glance from http://www.w3.org/2009/cheatsheet/#wcag2
Perceivable
Provide text alternatives for non-text content.
Provide captions and alternatives for audio and video content.
Make content adaptable; and make it available to assistive technologies.
Use sufficient contrast to make things easy to see and hear.
Operable
Make all functionality keyboard accessible.
Give users enough time to read and use content.
Do not use content that causes seizures.
Help users navigate and find content.
Understandable
Make text readable and understandable.
Make content appear and operate in predictable ways.
Help users avoid and correct mistakes.
Robust
Maximize compatibility with current and future technologies.
7 Steps to Make Computers Accessible for the Elderly http://www.makeuseof.com/tag/7-steps-to-make-computers-accessible-for-the-elderly/
Screen Resolution
Contrast
Sizes
Start menu buttons
Magnifier
Keystrokes
Mouse
Web Accessibility Perspectives: Explore the Impact and Benefits for Everyone http://www.w3.org/WAI/perspectives/ "Web accessibility is essential for people with disabilities and useful for all. Learn about the impact of accessibility and the benefits for everyone in a variety of situations."
[video demonstration] Skip to Main Content Link for Keyboard Users [NCSU] (YouTube 2:05) https://www.youtube.com/watch?v=Qjn0dymxuJk
Introduction to Web Accessibility http://www.w3.org/WAI/intro/accessibility.php
Website Accessibility [Penn State] http://accessibility.psu.edu/webpagetools/
7 Things You Should Know About IT Accessibility [EDUCAUSE] http://www.educause.edu/library/resources/7-things-you-should-know-about-it-accessibility
Link to PDF: https://net.educause.edu/ir/library/pdf/EST1403.pdf
Understanding the Four Principles of Accessibility https://www.sbcc.edu/accessibilitystandards/techniques.php [taken from
What: Examples of Web Accessibility http://www.w3.org/standards/webdesign/accessibility#examples
Web Accessibility Gone Wild http://webaim.org/articles/gonewild/
Jim Thatcher http://jimthatcher.com/index.htm He is selling services, but he has a lot of excellent information on his site.
Web Design Group http://www.htmlhelp.com/ This was "founded to promote the creation of non-browser specific, non-resolution specific, creative and informative sites that are accessible to all users worldwide.
Survey of Web Accessibility Practitioners Results http://webaim.org/projects/practitionersurvey/
Global Audit of Web Accessibility [United Nations] http://www.un.org/esa/socdev/enable/gawanomensa.htm
508 Compliance: Preparing Presentations, Excel Files, Websites, and Multimedia Products [ERIC ED545253] http://eric.ed.gov/?q=508+compliance&id=ED545253
Accessibility Resources http://www.interactiveaccessibility.com/accessibility-resources
Web Accessibility Resources http://www.ataporg.org/webar.aspx
* Web Design References: Accessibility [University of Minnesota Deluth] http://www.d.umn.edu/itss/training/online/webdesign/accessibility.html Extremely comprehensive for web authoring!
Accessibility: Web Fundamentals https://developers.google.com/web/fundamentals/accessibility/
Web Accessibility Group for Higher Education (WAG): Global Accessibility Awareness Day (GAAD)
WAG - GAAD Event (May 2017): Accessibility Challenge and Solutions in Higher Education http://www.amacusg.gatech.edu/wag/GAAD
Recording - https://sas.elluminate.com/site/external/launch/nativeplayback.jnlp?sid=2015068&psid=2017-05-18.0800.M.2B2466933275C2538FA05EE8E82F13.vcr - You must log in to view recording, but anyone can log in.
Handout - 10 Challenges and Solutions for ICT Accessibility in Higher Education http://www.amacusg.gatech.edu/wag/10_Challenges_and_Solutions_for_ICT_Accessibility_in_Higher_Education
Accessibility & Usability [Drexel University] http://drexel.edu/identity/web/website-management/design-standards/accessibility-usability/
New Era of Digital Accessibility https://www.insidehighered.com/system/files/media/508_2017%20Accessibility%20Booklet-Accessible.pdf
14 Questions for an Ed Tech Web Accessibility Expert http://www.3playmedia.com/2015/10/14/14-questions-for-an-ed-tech-web-accessibility-expert/
The Access Manifesto [The introduction to i online book, Building Accessible Websites by Joe Clark] http://joeclark.org/book/sashay/serialization/AccessManifesto.html
See also Legal & Ethical Issues
US Web Design Standard (draft) https://standards.usa.gov/
Getting Started https://standards.usa.gov/getting-started/ "designed to set a new bar for simplicity and consistency across government services, while providing you with plug-and-play design and code."
* Visual Style [US Web Design Standard (draft)] https://standards.usa.gov/visual-style/ "A typography suite and color palette designed to meet the highest standards of usability and accessibility, while setting a consistent visual voice of credibility, warmth, and ease-of-use across U.S. government digital platforms." (includes an excellent example of need for focus control..)
Website Content Accessibility Guidelines http://www.essentialaccessibility.com/ict-compliance
Illinois Information Technology Accessibility Act
Standards http://www.dhs.state.il.us/IITAA/IITAAStandards.html
Implementation Guidelines http://www.dhs.state.il.us/IITAA/IITAAWebImplementationGuidelines.html
(correct title) [University of Illinois at Urbana-Champaign] IITAA Implementation Guidelines for Web-Based Information and Applications http://www.dhs.state.il.us/IITAA/IITAAWebImplementationGuidelines.html
10 Tips for Creating Accessible Web Content with WCAG 2.0 [Webinar Recording from 3PlayMedia] http://www.3playmedia.com/how-it-works/webinars/wcag-05-21-2015/
Accessible Web Pages [University of Kansas] http://content.accessibility.drupal.ku.edu/accessible-web-pages
Web Accessibility Tutorials [W3C] http://www.w3.org/WAI/tutorials/
Introduction to Understanding WCAG 2.0 http://www.w3.org/TR/UNDERSTANDING-WCAG20/intro.html
Web Accessibility Tutorials and Presentations http://www.w3.org/WAI/train.html
Tutorials Overview http://www.w3.org/WAI/tutorials/
Before and After Demonstration: Improving a Web site using Web Content Accessibility Guidelines (WCAG) 2.0 http://www.w3.org/WAI/demos/bad/
The Essential Guide to Digital Accessibility [Deque] http://accessibility.deque.com/essential-guide-digital-accessibility
Web Accessibility 101 [45 minute on-demand webinar by Deque] http://www.deque.com/web-accessibility-101/
Web Accessibility - What not to do [really a how-to] http://jimthatcher.com/whatnot.htm
Web Accessibility Group (WAG) for Higher Education: Monthly Meetings http://www.amacusg.gatech.edu/wag/Monthly_Meetings This includes the Recordings and Resource Links for each of their meetings - excellent work! 1st Wednesday of each month
Accessible Information Technology Group [University of Illinois at Urbana-Champaign] http://disability.illinois.edu/academic-support/aitg
AccessDL (Center on Accessible Distance Learning) www.uw.edu/doit/accessdl
The U.S. Access Board https://www.access-board.gov/ This is a "federal agency that promotes equality for people with disabilities through leadership in accessible design and the development of accessibility guidelines and standards for the built environment, transportation, communication, medical diagnostic equipment, and information technology."
Web Accessibility and Development Glossary https://www.joedolson.com/glossary.php
Accessibility Dictionary [NetMechanic] http://www.netmechanic.com/accessibility/glossary.shtml
[W3C] WAI (Printable) Glossary [Internal Working Draft, 1 March 2003] http://www.w3.org/WAI/GL/Glossary/printable.html
Web Accessibility 101 Glossary https://www.merlot.org/merlot/viewMaterial.htm?id=842887
The Motive Web Design Glossary http://www.motive.co.nz/glossary/web-access.php Note: ‘References and further reading’ at the bottom looks especially good
See Accessibility Checklists page [CONSIDER NEW NAME.... Evaluation Tools]
There are a number of things you can do to check your site or an individual web page for compliance. There are checklists and a wide variety of tools. Some tools are built into programs you already use; some online tools give you suggestions after you give the URL. Some of the tools that need to be downloaded are add-ons or extension to your browser(s) and some are standalone tools. There are plenty of free options, but the best way to check your site for accessibility is to have real users - especially individuals who use assistive/adaptive technology or alternative input options - use your site.
New links that I find but have not yet looked at closely enough to add to my lists.