July 2024

November 2024

University of Turku

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

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

All `id` attributes on a page must be unique, or accessible technologies used by the page 
can stop working.

## Example

The duplicate `id` here makes it unclear which label belongs to which input field:

```html
<label for="name">Your name</label>
<input id="name">

<label for="name">Company name</label>
<input id="name">
```

As a result, accessible technologies like screen readers can fail to read out the 
correct text, or may read out no text at all.

Similar issues can occur when using `aria-labelledby` and `aria-describedby`.

## How to fix

Ensure all `id` attributes on a page are unique. 

## More information

See [Technique H93](https://www.w3.org/TR/2016/NOTE-WCAG20-TECHS-20161007/H93) 
for more information.

duplicate-id

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

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

People using screen readers are not able to see the layout of a form. To make forms
accessible, they must define explicit text labels for each form control. 

Usually the best solution is to use a `<label>` element. The label may be linked to 
by the form control:

```html
<label for="name">Full name</label>
<input type="name" id="name">
```

or the `<label>` can be wrapped around the form control:

```html
<label>
    Full name <input type="name">
</label>
```

Buttons are different, as their labels are specified by the code for the button, e.g.

```html
<input type="submit" value="Send message">
<button>Send message</button>
```

Alternatively ARIA attributes, such as `aria-label` may be used, but this information
will not be conveyed to visual users. For more information, see [W3C's guide to labeling controls](https://www.w3.org/WAI/tutorials/forms/labels/).

Hidden input fields (`<input type="hidden">`) do not require labels.
Note that the `placeholder` attribute 
[should not be used as an alternative to a label](https://www.w3.org/TR/html/sec-forms.html#the-placeholder-attribute),
nor should the `title` attribute.

## Custom roles

Note that this check considers the underlying accessible role of an element, which can be 
different from the tag itself.

For example, this `<div>` has a `role` of `button`, and so is expected to have a label, like
a button would.

```html
<div role="button"></div>
```

form-control-labels

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)

identify-input-purpose

Avoid opening links in a new tab or window. Where you must do this, include an explanation
in the text of the link.

## Why this matters

Opening links in a new tab or window breaks the back button and can be disorientating for 
novice web users, and the visually impaired. Generally you should avoid opening links in a
new tab or window, but if you have to, you should include text explaining that this will happen.

## How to fix

An explanation must be clear in the accessible text for the link. For example:

```html
<a href="products.html" target="_blank">
    Products (opens in new window)
</a>
```

Or, for an image inside a link:

```html
<a href="products.html" target="_blank">
    <img src="products.jpg" alt="Products (opens in new window)">
</a>
```

Rather than updating all of your links manually to do this, you can add a simple CSS
selector, such as:

```css
a[target="_blank"]:after {
    content: " (opens in new window)";
}
```

Note that doing this with an icon, is not sufficient to pass this check. The text must be
readable by screen readers.

Alternatively you can override the link text for accessible technologies (like screenreaders),
so that the appearance of the link does not change. For example:

```html
<a href="products.html" target="_blank" aria-label="Products (opens in new window)">
    Products
</a>
```

Note that if you do this, the `aria-label` will replace the text content of the link completely,
so it must still make sense in isolation.

## Terminology

Although it is common to say "opens in new window", almost all browsers now use tabs, and
so this terminology is potentially confusing. You may prefer: "opens in new tab".

## Methodology

1. Silktide considers all links on a page with a `target` attribute of `_blank`.
2. For each link, Silktide considers the screen-readable text of the link, which includes:
   * The text content of the link
   * Any `alt` text inside any images inside the link
   * Any `aria-label` or `aria-labelled-by` text
   * The `content` of the pseudo-elements `:before` and `:after`
3. This text is analysed for the presence of common text, including "opens new tab"
    and "opens new window". If the text is not found, the link fails the test.

## Further reading

Generally best practice is to avoid opening links in a new tab or window.  

The W3C provides detailed guidance on 
[when opening a link in a new window may be appropriate](https://www.w3.org/TR/WCAG20-TECHS/G200.html).

link-text-explains-open-in-new-window

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

When specifying accessible names via `aria-labelledby`, ensure that the 
label elements exist.

## Explanation

Accessible names are required for many parts of a page, including form controls.
One way to accomplish this is to use `aria-labelledby` to specify the ID or IDs of 
other elements which contain a label. For example:

```html
<h2 id="dialog-labell">Important message!</h2>
<dialog aria-labelledby="dialog-label">
```

In this example, the `aria-labelledby` for the `<dialog>` points to an ID of `dialog-label`,
which doesn't exist. The heading it refers to instead has an ID of `dialog-labell`, presumably 
a typo.

## Why this matters

It isn't usually clear when an accessible name is broken, even during user testing.

This check helps to identify where an element clearly intended to have a label, but
that label is missing.

When a label is broken, it may be impossible for a user of assistive technologies
to understand what that element does.

missing-aria-labelled-by

Every page should have a clearly defined heading, known as a "H1" (Heading 1).

A `H1` is the main heading of the page. It helps accessibility by allowing uses to
skip to the main content of the page. It helps all users identify what the page is about. 
It helps SEO by giving special emphasis to the topic of the page.

It is not enough to simply include large text. Headings must be coded 
[semantically](https://html.com/semantic-markup/) as `<h1>` tags, like so:

```html
<h1>This is a heading</h1>
```

Note that headings must contain some machine readable text to be considered valid. 
For example, this heading is not valid:

```html
<h1>
    <img src="company-logo.png">
</h1>
``` 

But with the addition of `alt` text, this heading is valid:

```html
<h1>
    <img src="company-logo.png" alt="About Company Inc.">
</h1>
``` 

Generally we recommend you just use plain text for your headings.
See [Technique H42](https://www.w3.org/TR/WCAG20-TECHS/H42) for more details.

missing-h1

Bookmarks (also known as outline entries) should be applied to long PDFs to 
provide a hierarchical overview of the document to help aid navigation. 

WCAG guidelines do not specify how many pages are required to be classified as a 
long PDF. Because of this Silktide treats PDFs of 21 or more pages as long. 
This matches [Adobe Acrobat](https://helpx.adobe.com/acrobat/using/create-verify-pdf-accessibility.html?trackingid=KACNN#Bookmarks) 
interpretation.  

See [WCAG](https://www.w3.org/TR/WCAG20-TECHS/pdf.html#PDF2) for advice.

pdf-long-document-requires-bookmarks

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

All PDFs must define a valid title. This must not be confused with the file name. 
See [PDF 18](https://www.w3.org/TR/WCAG20-TECHS/PDF18.html) for details.

pdf-no-title

PDFs need to be machine readable for accessibility software to be able to access them. 
Scanned documents or password protected ones are usually not machine readable.

pdf-not-machine-readable

All pre-recorded audio and video should provide appropriate captions. This allows people who are deaf 
or hard of hearing to use the media. 

Captions should provide the part of the content available via the audio track. Captions not only include 
dialogue, but identify who is speaking and include non-speech information conveyed through sound, 
including meaningful sound effects.

See [Understanding WCAG Success Criterion 1.2.2](https://www.w3.org/TR/UNDERSTANDING-WCAG20/media-equiv-captions.html).

prerecorded-captions-alternative

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
	Fix missing ARIA label IDs WCAG 2.0 A 1.3.1	0%
	Ensure pages don't scroll in two dimensions on small screens WCAG 2.1 AA 1.4.10	43.7%
	Ensure pages don't require zooming and 2D scrolling on small screens WCAG 2.1 AA 1.4.10	91.6%
	Ensure content is not too difficult to understand WCAG 2.0 AAA 3.1.5	42%
	Ensure interactive components are far enough apart WCAG 2.2 AA 2.5.8	74.1%

University of Turku

Accessibility

WCAG Levels

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