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Screen reader users will see links on a page listed without context, 
so you should ensure the same link text is not used to point to different web
addresses.

For example:

```html
<p>
    Learn the latest about our products: 
    <a href="/products/news">News</a>
</p>

<p>
    Learn the latest about our services: 
    <a href="/company/news">News</a>
</p>
``` 

To a screen reader who is listing links, they will only hear:

* News
* News

These links appear to be the same, but they both behave differently. 
One solution, which doesn't require the page design to change, is to add an 
`aria-label` for each link:

```html
<p>
    Learn the latest about our products: 
    <a href="/products/news" aria-label="Product news">News</a>
</p>

<p>
    Learn the latest about our services: 
    <a href="/company/news" aria-label="Company news">News</a>
</p>
``` 

Which will be heard as:

* Product news
* Company news

To pass this checkpoint, make sure that links which point to different pages 
have distinct text inside them, or that they specify ARIA labels (`aria-labelledby` or
`aria-label`), or they use hidden text only visible to screen readers
(e.g. `<span class="sr-only">...</span>`) to distinguish them from each 
other.

If links point to the same page (e.g., they redirect or use tracking
parameters, but are functionally equivalent to the user) you can ignore
this issue.

a-duplicate-link-text-for-different-destinations

To comply with the strictest accessibility standard (WCAG AAA), the colour of text must 
strongly contrast with its background color, so that people with significant visual impairments 
can read it.

The [contrast ratio](https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html#contrast-ratiodef)
must be at least 7:1 for body text, and 4.5:1 for large text.

A far less demanding version of this check (1.4.3) exists for WCAG AA. All websites should aim to 
meet the easier AA standard at a minimum. The AAA standard is desirable but far more challenging,
and may not be practical for your website.

aaa-text-contrast

All table headers should define a valid `scope` attribute, which tells assistive technologies
what the header refers to.

For example:

```html
<table>
    <thead>
    <tr>
        <th scope="col">Name</th>
        <th scope="col">Age</th>
    </tr>
    </thead>
    <tbody>
    <tr>
        <td>Bob</td>
        <td>35</td>
    </tr>
    <tr>
        <td>Sue</td>
        <td>45</td>
    </tr>
    </tbody>
</table>
```

In this example, the `scope` attribute indicates the two `<th>` cells are column 
headers, which allows assistive technologies to read out those headers alongside
each `<td>` cell. 

Without this information, the structure of the table is only apparent to people
who are able to see it.

add-scope-attribute-to-table-headers

Links must be defined in a specific way to be accessed by screen readers, which are used by 
blind and the partially-sighted.

To work with accessibility technologies, links must contain both machine-readable text, and 
a `href` attribute. If a link is not actually
pointing to a page or part of a page, it should be replaced with another semantic element, such
as a `button`, or the `<a>` tag should have a role of `button`. 

For example:

```html
<a href="/about">About us</a>
```

If the link contains _nothing but an image_, that image should specify alternative text, e.g.

```html
<a href="/apple">
    <img src="apple.png" alt="Apple">
</a>
```

Before HTML5, an anchor was often used to create a target to link to, e.g.

```html
<a name="example"></a>
```

This is not supported in HTML5, and the use of anchors for targets is discouraged. Use an `id`
attribute on a non-anchor tag instead, e.g.

```html
<div id="example"> ... </div>
```

Empty links (e.g. `<a></a>`) are often incorrectly used for buttons or controls in a
JavaScript application. In these cases, you should usually define the link as having a more appropriate
role, e.g. as a button. To do this, use the `role` attribute (e.g `<a role="button">`), or replace 
the `<a>` tag with a more appropriate tag, such as `<button>`.

For more details, see [Technique H91](https://www.w3.org/TR/2016/NOTE-WCAG20-TECHS-20161007/H91)
and learn about [ARIA roles](https://www.sitepoint.com/how-to-use-aria-effectively-with-html5/).

bad-anchor

Most content should be written so people with a lower secondary level of education can understand it.
Where this is not possible, supplemental content or an alternative version should be provided.

This check highlights pages with a reading age of 16 years or higher. Only pages with at least 100 words
of content (excluding navigation, footers, etc) are considered.  

For more information, see [WCAG SC 3.1.5](https://www.w3.org/TR/UNDERSTANDING-WCAG20/meaning-supplements.html).

ensure-reading-ability-is-not-advanced

All interactive components on a page, such as buttons or fields, should ideally be large enough 
to be easily used by people with motor impairments. 

This ensures people with motor impairments can easily click or tap on the element.

The recommended size is 44 x 44 CSS pixels, with some exceptions:

* **Equivalent available** - the functionality provided by
  the control is available elsewhere, and large enough, on the same page.
* **Inline text** - the control appears inside a sentence or block of text. 
* **User Agent control** - the size of the target is determined by the user agent 
  and is not modified by the author. Generally this is not the case for web content.
* **Essential** - the size of the target is essential to the information being conveyed,
  e.g. a tutorial demonstrating what a small button looks like. This exception is rare.

## Applying this check

Nearly all websites will fail this check by default. The minimum size requirement
is larger than most links and controls on most websites.

This is the much stricter version of the WCAG 2.2 AA check for target size. Most websites
should focus on the AA check before considering this AAA check:

* [Target Size (Minimum)](https://w3c.github.io/wcag/understanding/target-size-minimum.html)

## Methodology

This check is run on both the mobile and desktop versions of every page. Results
for each may differ.

1. All interactive elements are identified, including buttons, links, and form controls. 
2. If an element is preceded or followed directly by a non-empty text node, the control
   is ignored.
3. If an element is not normally visible, it is ignored. This includes elements which 
   are positioned offscreen or cropped (e.g. for 'screen-reader only' text).
4. If an element is a link, and another visible link on the page points to the same URL, with 
   that other link meeting the size requirements, the element is ignored.
5. Otherwise, the element must have a minimum size of 44 x 44 CSS pixels.

## Troubleshooting

Silktide only records the first 100 instances of a failure on a page. Because failures
of this check are common, it is possible that your page has more than 100 failures, but
only the first 100 will be shown.

## Further reading

* [Target Size (Enhanced)](https://www.w3.org/WAI/WCAG22/Understanding/target-size-enhanced)

ensure-reasonable-target-size

When viewed on small screens (like mobile phones) content should be large enough to 
read without being zoomed-into and scrolled in two dimensions.

WCAG 2.1 specifically requires this for:

+ Vertical scrolling content at a width equivalent to 320 CSS pixels
+ Horizontal scrolling content at a height equivalent to 256 CSS pixels

This issue almost always indicates that the webpage has not been designed
to work on mobile devices at all.

extreme-zoom-scrolling

An image with empty alternative text (e.g. `<img alt="">`) should not specify a 
`title` attribute, or if specified, the `title` should be empty.

For example, this is invalid:

```html
<img src="apple.png" alt="" title="This is an apple">
```

img-with-empty-alt-but-has-title

Do not link to an anchor on the page that does not exist. For example:
linking to `#content` without a valid destination such as `<body id="content"></body>`.

A common web design pattern is to use a named anchor to show an element via JavaScript, e.g.

```html
<a href="#foo" onclick="$('.bar').toggle();">Click me</a>
<div class="bar">
    This is some content.
</div>
``` 

In these cases, the anchor (`#foo`) should point to the `id` of the hidden element:

```html
<a href="#foo" onclick="$('#foo').toggle();">Click me</a>
<div id="foo">
    This is some content.
</div>
```

This way the semantic intent of the link is preserved, even without JavaScript. 
Note that doing so may require modification to your script, to prevent automatic 
scrolling to the named anchor.

linking-to-anchor-on-page-that-does-not-exist

PDFs should have a default document language set to help render text accurately and help screen readers pronounce words correctly. 
See [WCAG](https://www.w3.org/TR/WCAG20-TECHS/pdf.html#PDF16) for reference.

pdf-missing-default-language

PDF files should have headings.
 See [WCAG](https://www.w3.org/TR/WCAG20-TECHS/pdf.html#PDF9)

pdf-missing-headings

PDFs need to be tagged in a valid reading order for accessibility. See [Adobe's guide](https://helpx.adobe.com/uk/acrobat/using/creating-accessible-pdfs.html#tag_the_pdf) and [WCAG](https://www.w3.org/TR/WCAG20-TECHS/pdf.html#PDF3) for advice.

pdf-must-be-tagged

When viewed on small screens (like mobile phones) content must fit without 
requiring scrolling in two dimensions.

WCAG 2.1 specifically requires this for:

+ Vertical scrolling content at a width equivalent to 320 CSS pixels
+ Horizontal scrolling content at a height equivalent to 256 CSS pixels

Except for parts of the content which require two-dimensional layout for usage or meaning,
such as a maps application.

Priority	Recommendation	Progress
	Ensure pages don't scroll in two dimensions on small screens WCAG 2.1 AA 1.4.10	77%
	Avoid linking to anchors that do not exist WCAG 2.0 A 2.4.1	33.3%
	Tag all PDFs WCAG 2.0 A 1.3.1	50%
	Ensure pages don't require zooming and 2D scrolling on small screens WCAG 2.1 AA 1.4.10	95.8%
	Ensure content is not too difficult to understand WCAG 2.0 AAA 3.1.5	71%

Schouwen-Duiveland

Accessibility

WCAG Levels

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