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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 dialogs (sometimes knows as 'pop up windows') should declare an accessible label that
can be read out by screen readers.

To do this, use `aria-label` to specify a label, or `aria-labelledby` to point to the `id`
of an element that contains text describing the modal, e.g.:

```html
<div role="dialog" aria-labelledby="title">
    <div id="title">
        This is a dialog
    </div>
</div>
```

The above example dialog has a label of `This is a dialog`.

dialog-labels

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

wcag-22.score

wcag-22-a.score

wcag-22-aa.score

wcag-22-aaa.score

website.pages

website.documents

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

### Not enough contrasting pixels change

The [Success Criterion](https://w3c.github.io/wcag/understanding/focus-appearance.html) specifies a minimum area 
for the contrasting portion of the focus indicator, which is equivalent to a 2 CSS pixel border around the component.

From the requirements:

> "The easiest and most common way to meet this requirement is to use a solid outline around the component. 
> The outline must be at least 2px thick."

In practice, many websites use alternatives to this, such as a thick border along one edge. A problem with 
that approach is it is often dependent upon the length of that one edge, which for text links can vary dynamically.

See [Sara Soueidan](https://www.sarasoueidan.com/blog/focus-indicators/#2.-minimum-contrasting-area) for a good
write-up of this concept.

To comply with this Success Criterion, we recommend adding a 2px border around all edges.

Note an earlier draft of this Success Criterion has a more generous allowance here, which is not the case for the
final version.

### 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

* [WCAG 2.4.13](https://www.w3.org/WAI/WCAG22/Understanding/focus-appearance.html)
* [Minimum Contrasting Area explained (Sara Soueidan)](https://www.sarasoueidan.com/blog/focus-indicators/#2.-minimum-contrasting-area)

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

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

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

Ensure that long PDF documents incorporate bookmarks to facilitate easy navigation.

## What this means

In the context of PDFs, bookmarks are navigational tools that act like an interactive table of contents. 
They allow users to quickly jump to specific sections, chapters, or points of interest within the document. 
This feature is particularly important in longer PDFs, where scrolling through the entire document to find 
specific information can be time-consuming and inefficient.

## Why it matters

1. **Accessibility**: For users with disabilities, especially those using screen readers, bookmarks provide a way to navigate through the document without having to linearly read through all the content.
2. **User Convenience**: Bookmarks significantly enhance the user experience by allowing quick access to different sections of the document.
3. **Efficiency**: In professional or academic settings, bookmarks help in referencing and reviewing long documents more efficiently.

## How to fix

1. **Identify Key Sections**: Determine the main sections or chapters of your PDF that would benefit from bookmarks.
2. **Create Bookmarks**: Use a PDF editing tool to create bookmarks at these key sections. Ensure that the bookmarks are clearly labeled to accurately reflect the content they link to.
3. **Organize Hierarchically**: If your document has sub-sections, consider creating a hierarchical structure in your bookmarks for better organization.

## Testing Methodology

Silktide scans the PDF to identify the presence of bookmarks in documents exceeding 21 pages.

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's](https://helpx.adobe.com/acrobat/using/create-verify-pdf-accessibility.html?trackingid=KACNN#Bookmarks)
interpretation.

### Limitations
- **Page Threshold**: Silktide uses a predetermined page count to trigger this check, which may not always align with the user's definition of a 'long' document.
- **Bookmark Relevance**: While Silktide can detect the presence of bookmarks, it does not assess their relevance or accuracy in representing the document's content.

## Further Reading

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

pdf-long-document-requires-bookmarks

Ensure that PDF documents specify a default language, so that assistive technologies can accurately 
interpret their contents.

## What this means

Specifying a default language for a PDF means setting the primary language in which the document's content is written. 
This setting informs users and assistive technologies about the language the content is presented in, aiding in 
proper interpretation and pronunciation.

## Why it matters

1. **Accessibility**: Screen readers rely on language settings to provide correct pronunciation, making it essential for non-native speakers and individuals using text-to-speech software.
2. **User Experience**: Specifying the language helps in providing a better reading experience as it enables features like spell check and grammar tools to function correctly.
3. **Global Compliance**: Setting a default language is a requirement under various international accessibility standards, like the Web Content Accessibility Guidelines (WCAG).

## How to fix

1. **Check Document Properties**: Open the document properties in your PDF editor and navigate to the language setting.
2. **Set the Default Language**: Choose the appropriate language from the list provided or enter it manually if it's not listed.

## Testing Methodology

Silktide analyzes the document properties of the PDF to verify if a default language is specified.

### Limitations
- **Language Accuracy**: While Silktide can detect the presence of a language setting, it does not assess the accuracy of the language in relation to the document's content.
- **Multilingual Documents**: For documents containing multiple languages, Silktide might only detect the primary language set in the document properties.

## Further Reading

- [WCAG PDF 16](https://www.w3.org/TR/WCAG20-TECHS/pdf.html#PDF16)
- [Setting Language in PDF Documents](https://www.adobe.com/accessibility/pdf/pdf-accessibility-overview.html)
- [Understanding WCAG: Language of Page](https://www.w3.org/TR/UNDERSTANDING-WCAG20/meaning-doc-lang-id.html)

pdf-missing-default-language

Ensure that PDF documents specifies headings for accessibility.

## What this means

Specifying headings in a PDF involves clearly defining tagged heading elements within 
the document. These headings are used to structure the content, similar to how headings 
are used in web content (like HTML). 

## Why it matters

1. **Accessibility**: Headings are crucial for screen readers and other assistive technologies. They allow users with visual impairments to navigate the document more easily.
2. **Document Structure**: Clearly defined headings help in organizing the content, making it more understandable and navigable for all users.
3. **Search Efficiency**: Proper headings improve the document's searchability, enabling users to find information more quickly.

## How to fix

1. **Use Styles in Document Creation**: When creating a document, use heading styles (like Heading 1, Heading 2, etc.) in your word processor before converting it to a PDF.
2. **Edit Existing PDFs**: If your PDF is already created, use a PDF editor to add or modify heading tags. Ensure that the headings are in a logical hierarchical order.

## Testing Methodology

Silktide flags PDFs that don't contain a single tagged heading.

## Further Reading

- [WCAG PDF9](https://www.w3.org/TR/WCAG20-TECHS/pdf.html#PDF9)
- [Creating Accessible PDFs](https://www.adobe.com/accessibility/pdf/pdf-accessibility-overview.html)
- [PDF Accessibility - Defining PDF Accessibility](https://www.webaim.org/techniques/acrobat/)

pdf-missing-headings

PDF documents must be tagged to ensure accessibility and compliance with digital standards.

## What this means

Tagging in a PDF involves adding hidden metadata that outlines the structure and content of the document. These tags function similarly to HTML tags, describing elements like headings, paragraphs, lists, and tables. They are crucial for screen readers and other assistive technologies to interpret the content correctly.

## Why it matters

1. **Accessibility**: Tagging makes PDFs accessible to individuals with disabilities, allowing assistive technologies to read and navigate the document effectively.
2. **Legal Compliance**: Various laws and regulations require digital content, including PDFs, to be accessible. Failure to comply can lead to legal complications.
3. **Usability**: Tagged PDFs are more user-friendly, providing better navigation and search capabilities for all users.

## How to fix

1. **Use Tag-enabled PDF Creators**: Create or convert documents using software that supports tagging, like Adobe Acrobat or Microsoft Word.
2. **Manually Add Tags**: If your PDF isn't tagged, use a PDF editor's accessibility tools to add tags. This includes setting a logical reading order and adding alternative text for images.
3. **Consult Guidelines**: Follow best practices outlined in WCAG or similar guidelines for effective tagging.

## Testing Methodology

Silktide looks at the PDF and flags it if it doesn't contain tags.

## Further Reading

- [Adobe's Guide to PDF Accessibility](https://www.adobe.com/accessibility/pdf/pdf-accessibility-overview.html)

pdf-must-be-tagged

Ensure each PDF document has a formally defined title.

## What this means

A PDF title, typically found in the document properties, acts as the official name of the document. This title is used by screen readers and other assistive technologies to provide a clear understanding of the document's content at the outset. It's different from any title or heading text that might appear within the content of the PDF itself.

## Why it matters

1. **Accessibility**: Screen reader users often hear the document title first when they open a PDF. A clear, descriptive title helps them understand what the document is about.
2. **Searchability and Organization**: A proper title makes it easier to search for and organize documents on a computer or network.

## How to fix

1. **Set the Title in Document Properties**: In your PDF editor, access the document properties section and ensure there is a title that accurately reflects the content of the PDF.
2. **Use Descriptive Titles**: Avoid vague titles. Instead, choose titles that clearly and concisely convey the subject or purpose of the document.

## Testing Methodology

Silktide checks the document properties of a PDF to verify that a title is 
specified and not empty.

### Limitations
- **Title Relevance**: While Silktide can detect the presence of a title, it does not evaluate the title's relevance or accuracy in representing the document's content.

## Further Reading

- [WCAG - PDF 18](https://www.w3.org/TR/WCAG20-TECHS/PDF18.html)
- [Setting Titles in PDF Documents](https://www.adobe.com/accessibility/pdf/pdf-accessibility-overview.html)

Priority	Recommendation	Progress
	Ensure text has sufficient contrast (AA) WCAG 2.0 AA 1.4.3	40%
	Ensure dialogs have labels WCAG 2.0 A 1.3.1	33.3%
	Aim for text to have very high contrast (AAA) WCAG 2.0 AAA 1.4.6	0%
	Aim for large interactive controls WCAG 2.1 AAA 2.5.5	41%

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Accessibility

WCAG Levels

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