When someone describes a site as "accessible", they mean that any user can use all its features and content, regardless of how the user accesses the web — even and especially users with physical or mental impairments.

• Sites should be accessible to keyboard, mouse, and touch screen users, and any other way users access the web, including screen readers and voice assistants like Alexa and Google Home.
• Applications should be understandable and usable by people regardless of auditory, visual, physical, or cognitive abilities.
• Sites should also not cause harm: web features like motion can cause migraines or epileptic seizures.

To get the most out of this module, it would be a good idea to either work through at least the first two modules of the HTML, CSS, and JavaScript topics, or perhaps even better, work through the relevant parts of the accessibility module as you work through the related technology topics.

Accessibility is the practice of making your websites usable by as many people as possible. We traditionally think of this as being about people with disabilities, but the practice of making sites accessible also benefits other groups such as those using mobile devices, or those with slow network connections.

You might also think of accessibility as treating everyone the same, and giving them equal opportunities, no matter what their ability or circumstances. Just as it is wrong to exclude someone from a physical building because they are in a wheelchair (modern public buildings generally have wheelchair ramps or elevators), it is also not right to exclude someone from a website because they have a visual impairment. We are all different, but we are all human, and therefore have the same human rights.

As you learn more about HTML — read more resources, look at more examples, etc. — you'll keep seeing a common theme: the importance of using semantic HTML (sometimes called POSH, or Plain Old Semantic HTML). This means using the correct HTML elements for their intended purpose as much as possible.

You might wonder why this is so important. After all, you can use a combination of CSS and JavaScript to make just about any HTML element behave in whatever way you want. For example, a control button to play a video on your site could be marked up like this:

Play Video

But as you'll see in greater detail later on, it makes sense to use the correct element for the job:

Play Video

Not only do HTML

Semantic HTML doesn't take any longer to write than non-semantic (bad) markup if you do it consistently from the start of your project. Even better, semantic markup has other benefits beyond accessibility:

1. Easier to develop with — as mentioned above, you get some functionality for free, plus it is arguably easier to understand.
2. Better on mobile — semantic HTML is arguably lighter in file size than non-semantic spaghetti code, and easier to make responsive.
3. Good for SEO — search engines give more importance to keywords inside headings, links, etc. than keywords included in non-semantic
   s, etc., so your documents will be more findable by customers.

CSS and JavaScript don't have the same immediate importance for accessibility as HTML, but they are still able to help or damage accessibility, depending on how they are used. To put it another way, it is important that you consider some best practice advice to make sure that your use of CSS and JavaScript doesn't ruin the accessibility of your documents.

Following on from the previous article, sometimes making complex UI controls that involve unsemantic HTML and dynamic JavaScript-updated content can be difficult. WAI-ARIA is a technology that can help with such problems by adding in further semantics that browsers and assistive technologies can recognize and use to let users know what is going on. Here we'll show how to use it at a basic level to improve accessibility.

As web apps started to get more complex and dynamic, a new set of accessibility features and problems started to appear. For example, HTML introduced a number of semantic elements to define common page features (