October 2024

November 2024

Gloppen

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 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

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

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

This is default behavior for all standard web controls, and so if this issue is appearing
it is because this default behavior has been disabled. Or alternatively, if you have written
your own custom controls, these will need styling to support focus states.

## How to fix

Links and form controls typically define an `outline` CSS style, which ensures
they are highlighted automatically, for example:

```css
input:focus (outline: 2px solid red);
``` 

If you choose to override or disable the default `outline`, you should specify an accessible 
alternative, such as a border or background color.

### 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.

### 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

* [WCAG 2.4.7](https://www.w3.org/WAI/WCAG22/Understanding/focus-visible.html)

ensure-focus-is-visible

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

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

Users must be able to magnify the contents of a web page by up to 200%. In modern 
browsers this is almost always possible unless the page chooses to disable it.

Websites should avoid using the meta viewport tag to disable pinch-to-zoom. This behavior
is highly discouraged for accessibility and usability on mobile devices.

Generally the code causing this issue looks like this:

```html
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />
```

Here the use of `user-scaleable=no` asks the browser not to allow user zoom. 

iOS no longer allows websites to disable pinch-to-zoom, and ignores this part of the
viewport tag. Therefore to replicate this issue you must use an Android device.

ensure-text-can-resize

Forms should always contain a submit button, otherwise some people using
accessible technologies may not be able to submit the form.

Submit buttons are `<input>` elements with a type attribute of `submit` or
`image`, or `<button>` elements with type `submit`. 

## Rationale 

Many users expect to be able to press enter in a form to submit it. However,
this is not always possible.

Users of some assistive technologies may (depending on the technology) only
be able to press a button to submit the form. In the absence of a submit
button, the user may not be able to submit the form.

In addition, the absence of a submit button suggests that the form may 
provide an automatic 'change of context', i.e. major change to the user 
interface without the user choosing to do so. This can be highly disorientating
to some users.

## Further reading

See [Technique H32](https://www.w3.org/TR/WCAG20-TECHS/H32.html).

form-submit-required

An `<img>` element inside a link must not specify alternative text that duplicates the
content of a text link inside or beside it.

For example, this code should be avoided:

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

Accessible technologies will tend to see this as "Apple Apple". The correct behaviour is to
specify either a null (empty) `alt` attribute:

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

or to hide the image via `aria-hidden`:

```html
<a href="/apple">
    <img src="apple.png" aria-hidden="true">
    Apple
</a>
```

# Learn more

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

See the [WAI Tutorial on decorative images](https://www.w3.org/WAI/tutorials/images/decorative/).

img-duplicate-alt

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

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

pdf-missing-headings

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

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 controls clearly indicate when they are selected WCAG 2.2 AA 2.4.11	4.4%
	Ensure controls change appearance when they are selected WCAG 2.0 AA 2.4.7	2%
	Ensure PDFs have a title WCAG 2.0 A 2.4.2	0%
	Ensure text has sufficient contrast (AA) WCAG 2.0 AA 1.4.3	23.2%
	Ensure pages don't scroll in two dimensions on small screens WCAG 2.1 AA 1.4.10	77%

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