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British Film Institute

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 WCAG AA, the colour of text must sufficiently contrast with
its background color, so that people with moderate 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 4.5:1 for body text, and 3:1 for large text.

A much more demanding version of this check (1.4.6) exists for WCAG AAA. Ignoring an issue in this check 
will also ignore it in that check, and vice versa.

aa-text-contrast

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

Two adjacent links should not point to the same destination. You almost always want to combine the 
two links.

For example, it is quite common to link an image and text together like this:

```html
<a href="news.html">
    <img src="photo.jpg" alt="" />
</a>
<a href="news.html">
    News
</a>
``` 

These adjacent links should be combined like so:

```html
<a href="news.html">
    <img src="photo.jpg" alt="" />
    News
</a>
``` 

Links to `#` are ignored, as these are nearly always placeholders for JavaScript, e.g.:

```html
<a href="#" onclick="approve()">
    OK
</a>
<a href="#" onclick="reject()">
    Cancel
</a>
```

# Justification

Many users of assistive technology are only able to experience content sequentially - that is, they must
step through each part of the page, one part at a time. Often this is a slow process, potentially 
hampered by a physical impediment.

Stepping through redundant links is time consuming; for example users of a screen reader must 
hear each link read aloud in turn. 

This also simplifies your code. 

# Methodology

1. Find all links (`<a>` tags) on the page.
2. Ignore links pointing to `#`, as these are usually placeholders for JavaScript.
3. Flag links which are (a) separated only by whitespace and (b) which point to the 
   same absolute URL.  

# Learn more

Read about [Technique H2](https://www.w3.org/TR/WCAG20-TECHS/H2) on how to combine
an adjacent image and texts links.

duplicate-adjacent-link

All controls on the page - including links, buttons, and fields - should clearly 
indicate when they have been selected by the keyboard.

This is a stricter version of [WCAG 2.4.7](https://www.w3.org/WAI/WCAG21/Understanding/focus-visible.html),
which requires that the focus indicator is visible, but doesn't specify how clearly
it should be visible.

You can confirm this yourself by loading a webpage and using the Tab key to navigate 
through it. Anything you can select should clearly alter its appearance when selected. 
For example, a text field might change color, or have a distinctive border applied. 

## The requirements

The [official requirements](https://w3c.github.io/wcag/understanding/focus-appearance.html) are 
complicated. A simplified version is:

* Surround the control with a solid outline
* The outline must have at least 3:1 contrast with its background
* The outline must have at least 3:1 contrast with its surroundings, or be at least 2px thick

The actual requirements allow for more variation, but generally require that you 
calculate the perimeter and/or area of the focus area, which can be very difficult.

## How to fix

Links and form controls should use a focus selector which contrasts with their
unfocused state, as well as any surroundings of the focus state. 

In practice, the easiest way to accomplish this is to use a two-color focus, like so:

```css
/* ensure high-contrast mode still has an indicator */
outline: 2px transparent solid;

/* Apply a thick yellow box-shadow with 
   a thin dark blue indicator in the middle */
box-shadow: 0 0 0 2px #F9F9D1, 0 0 0 4px #396196, 0 0 4px 8px #F9F9D1;
``` 

From [Technique C40](https://www.w3.org/WAI/WCAG22/Techniques/css/C40).

Using two contrasting colors guarantees that the focus state will be visible, 
regardless of the background or surrounding colors.

## Troubleshooting

### Elements appear to change in the browser

Focus states should be defined in CSS alone, and not require JavaScript to work. 

Try disabling JavaScript on the page, and see if focus is still visible. If it not, 
then the focus state won't work with assistive technologies that don't have a physical
keyboard, e.g. mobile phones.

Some more unusual means of implementing a focus state cannot be detected or measured
automatically. These include:

* Focus implemented via pseudo-elements - such as `::after` or `::before`. 
* Focus using `:focus-within` (JavaScript current provides no way to access these).
* Focus cascaded to child elements, e.g. a `<span>` inside an `<a>` tag. We detect
  some of these cases, but there are variations that we cannot detect.

Currently, there is no practical way to assess these focus states automatically.

### Elements over images not analyzed

Silktide cannot assess the contrast of elements that are over images. This is because
the contrast of an element is calculated by comparing the color of the element with the
color of the background. 

If the element is over an image, the background color is the
color of the image, which varies from pixel-to-pixel, and may vary further as the page
is resized, due to responsive design.

### Unexpected elements are focusable

You may be surprised to see tags like `<div>` or `<span>` being shown as focusable.
If an element has a `tabindex` of 0 or higher, it becomes focusable. Any HTML tag can be made 
focusable in this way, this is so that custom controls (e.g. your own drop-down menus, or 
sliders) can support keyboard navigation. [Learn more about tabindex on MDN](https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/tabindex).

## Further reading

This is part of the draft WCAG 2.2 specification and is subject to change.

* [WCAG 2.4.11](https://w3c.github.io/wcag/understanding/focus-appearance.html)

ensure-focus-appearance

When selecting a user interface component with the keyboard, the focus indicator must 
not be partly obscured by anything in front of it. This is the stricter version of this check for 
Level AAA.

## Why this matters

When using a keyboard, it is important that the user can see where they are on the page.
If the focus indicator is obscured, the user may not know where they are, and may not
be able to interact with the page.

## Examples

Most common examples include:

* Banners at the top or bottom of the page, such as cookie banners
* Fixed navigation bars
* Fixed footers
* Popup modals, such as cookie consent modals

## How to fix

With elements that cover part of the screen, such as cookie banners, ensure
that the user can scroll to see any content behind the banner, without having to close
the banner.

With popup modals, it should usually be impossible to focus anything behind the modal.
Most common modal frameworks will automatically trap focus within the modal, so that
this is impossible. Example: [Bootstrap Modal](https://getbootstrap.com/docs/5.2/components/modal/#live-demo).

## Further reading

This is part of the draft WCAG 2.2 specification and is subject to change.

* [WCAG 2.4.13](https://w3c.github.io/wcag/understanding/focus-not-obscured-enhanced.html)

ensure-focus-is-not-obscured-enhanced

All interactive components on a page, such as buttons or menus, should be far enough apart 
from other interactive areas, to avoid them being used by mistake. 

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

## 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 not normally visible, it is ignored. This includes elements which
   are positioned offscreen or cropped (e.g. for 'screen-reader only' text).
3. If an element is larger than 24 CSS pixels in both dimensions, it passes.
4. Otherwise, the element is compared to all other elements on the page.
5. The minimum horizontal gap between the element is calculated as 24 CSS pixels,  
   minus the width of the element.
6. The minimum vertical gap between the element is calculated as 24 CSS pixels,  
   minus the height of the element.
7. If another element falls within the minimum horizontal or vertical gap, the 
   element fails, unless both are links that point to the same place.

## Further reading

This is part of the draft WCAG 2.2 specification and is subject to change.

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

ensure-minimum-target-size

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

The purpose of a link should be clear from the text inside the link. Links like "learn more" are
not helpful to users with accessible technology.

Links should also avoid redundantly saying that they are links, e.g. "link to page" as screen
readers will read these out with the word "link" added, e.g. "link link to page".

Exceptions to these rules are allowed where the purpose of a link would be ambiguous to users 
in general.

link-purpose-a

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

Lists of related items should be written [semantically](https://html.com/semantic-markup/) as a 
list.

Usually this means rewriting these to use the `<ul>` or `<ol>` tags.

This allows assistive technologies to more easily navigate from item to
item, or past entire groups of links if the user wants to. 

## Examples 

### Navigation

This navigation:

```html
<a href="/about">About us</a>
<a href="/products">Products</a>
<a href="/contact">Contact us</a>
```

Should be rewritten as a list:

```html
<ul>
  <li><a href="/about">About us</a></li>
  <li><a href="/products">Products</a></li>
  <li><a href="/contact">Contact us</a></li>
</ul>
```

### Tables for content

This single-column table is redundant. There is no
value in placing the content in a table, which makes
it harder for screen reader users to interpret and interact
with.

```html
<table>
  <tr>
    <td>
      Banana
    </td>
  </tr>
  <tr>
    <td>
      Apple
    </td>
  </tr>
  <tr>
    <td>
      Pear
    </td>
  </tr>
</table>
```

Should be rewritten as a list:

```html
<ul>
  <li>Banana</li>
  <li>Apple</li>
  <li>Pear</li>
</ul>
```

## Justification

Users of assistive technologies, like screen readers, can skip an entire
list in one step. In some cases, they can even search inside a list. 

These aids are not available where links are written outside a list. 
Failing to use lists correctly can force users to have to step through
hundreds of items one at a time.

## Methodology

1. Any single-column tables are automatically considered 
   redundant lists. 
2. For non-table elements, recursively work down the page looking inside
   each element for links separated by minimal amounts of non-link text. 
   If the non-link text is below 30 characters 
   in length, we assume we're inside content that should be a list.
   Some exceptions are made, e.g. the presence of an `<hr>` would break
   out of the list.

## More information

See [Technique
H48](https://www.w3.org/TR/2016/NOTE-WCAG20-TECHS-20161007/H48) for
details.

mark-navigation-section-as-list

All images, video, audio and other media should specify appropriate
[alternative text](https://help.silktide.com/articles/alternative-text/).

For example:

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

Alternative text should be descriptive and useful. We recommend you read 
[this comprehensive guide to writing alternative text](https://webaim.org/techniques/alttext/)
by WebAIM.

The W3C also provide more information on how to satisfy this check in [Technique H37](https://www.w3.org/TR/WCAG20-TECHS/H37).

missing-alt

wcag-22.score

wcag-22-a.score

wcag-22-aa.score

wcag-22-aaa.score

website.pages

website.documents

Tables which contain information should have clear headers defined.  

In this example, the top row of the table is a header:

| Surname        | City          |
| -------------- | ------------- |
| Washington     | London        |
| Phoenix        | Arizona       |
| Austin         | Travis        |

Notice how without the header here, it would be almost impossible to understand 
what the individual values mean ("Washington" could be a city or a surname). 

It is not enough to just make the headers look differently, as accessible technologies will not 
recognize this (for example, a screen reader cannot 'see' different colors or fonts). 
Table headings must be defined using the `<th>` tag. 

This example shows how a table should use a `<th>` to mark cells as headings. Note the 
use of the `col` attribute, to specify these headings are for the _column_:

```html
<table>
  <tr>
    <th scope="col">First name</th>
    <th scope="col">City</th>
  </tr>
  <tr>
    <td>Washington</td>
    <td>London</td>
  </tr>
  <tr>
    <td>Phoenix</td>
    <td>Arizona</td>
  </tr>
  <tr>
    <td>Austin</td>
    <td>Travis</td>
  </tr>
</table>
```

Tables which are used purely for layout do not need to do this. However, 
[the use of tables for layout is strongly discouraged](https://www.lifewire.com/dont-use-tables-for-layout-3468941).
This check will ignore tables that it believes are purposely used for layout.

Learn more about [accessible table design (W3C)](https://www.w3.org/WAI/tutorials/tables/one-header/).

add-header-to-tables

When selecting a user interface component with the keyboard, the focus indicator must 
not be completely obscured by anything in front of it.

## Why this matters

When using a keyboard, it is important that the user can see where they are on the page.
If the focus indicator is obscured, the user may not know where they are, and may not
be able to interact with the page.

## Examples

Most common examples include:

* Banners at the top or bottom of the page, such as cookie banners
* Fixed navigation bars
* Fixed footers
* Popup modals, such as cookie consent modals

## How to fix

With elements that cover part of the screen, such as cookie banners, ensure
that the user can scroll to see any content behind the banner, without having to close
the banner.

With popup modals, it should usually be impossible to focus anything behind the modal.
Most common modal frameworks will automatically trap focus within the modal, so that
this is impossible. Example: [Bootstrap Modal](https://getbootstrap.com/docs/5.2/components/modal/#live-demo).

## Further reading

This is part of the draft WCAG 2.2 specification and is subject to change.

* [WCAG 2.4.12](https://www.w3.org/WAI/WCAG22/Understanding/focus-not-obscured.html)

ensure-focus-is-not-obscured-minimum

To comply with WCAG 2.1, fields must identify what their purpose is _programmatically_. If done correctly,
this allows browsers to help users fill in forms with known information, such as their name and email address.

This is accomplished via the `autocomplete` attribute, which should be set to a 
[supported value](https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/autocomplete) wherever
appropriate, e.g. 

```html
<label for="name">
  First Name
</label>
<input id="name" type="text" autocomplete="given-name">
```

For fields where `autocomplete` is not appropriate, e.g. due to security, or the field not matching the
specification, the specific field should be ignored.

## Methodology

* All fields which could support `autocomplete` (e.g. text fields)
  are checked. Other fields - like dropdown menus - are ignored.
* The [accessible name](https://www.w3.org/TR/accname-1.2/) of each field is considered. In most cases this
  will be the `<label>` for the field.
* If the name matches a known pattern the field 
  must have an appropriate `autocomplete` value specified.
  For example, an `<input>` with type `text` with a label of 
  "First Name" would be expected to have an autocomplete value 
  of `given-name` or similar.

Note that using `autocomplete="on"` is not sufficient to pass this check, a
specific named autocomplete value must be used. See the
[supported values](https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/autocomplete).

## Troubleshooting

If a field is a false positive, check whether the field has an 
appropriate accessible name (i.e. a `<label>` or `aria-label`).

If the label is incorrect, Silktide may assume that the field 
requires `autocomplete` where it does not. You should fix the 
label to avoid this.

Otherwise, you can simply ignore the specific field.

## More information

* [How to use HTML 5.2 attributes](https://www.w3.org/WAI/WCAG21/Techniques/html/H98)

Priority	Recommendation	Progress
	Ensure controls clearly indicate when they are selected WCAG 2.2 AA 2.4.11	22%
	Ensure focus is not fully obscured WCAG 2.2 AA 2.4.12	99.5%
	Write lists or groups of links semantically WCAG 2.0 A 1.3.1	0%
	Ensure content is not too difficult to understand WCAG 2.0 AAA 3.1.5	64.8%
	Avoid linking to anchors that do not exist WCAG 2.0 A 2.4.1	78.1%

British Film Institute

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WCAG Levels

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