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Ullensaker

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

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

All field sets should contain a legend which describes its contents.

A field set is a group of form controls, such as radio buttons, checkboxes, or text fields. The
`<fieldset>` element is used to group these controls together, and the `<legend>` element is used to
describe the contents of the field set.

Whenever the `<fieldset>` element is used, it must contain a valid `<legend>` element, which
describes the contents of the field group.

## Further reading

See [how to provide a description for groups of form controls using fieldset and legend elements](https://www.w3.org/TR/WCAG20-TECHS/H71).

add-legend-to-fieldset

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

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.

## How to fix

* Ensure all interactive elements are at least 24 CSS pixels wide and tall
* OR ensure there is at least 24 CSS pixels (minus the width and height of the element)
  between each interactive 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

* [Target Size (Minimum)](https://www.w3.org/WAI/WCAG22/Understanding/target-size-minimum.html)
* [Technique C42 - Using min-height and min-width to ensure sufficient target spacing](https://www.w3.org/WAI/WCAG22/Techniques/css/C42)

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

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

Links must be appear visually distinct from regular text. A common mistake is to make links
only differ subtly in color. Users with visual impairments cannot see these links.   

There are two ways to comply with this requirement:

1. You can make links appear differently from regular text without relying on color alone.
   For example, you can add an underline to your links. This makes links easy to identify, even
   to people who cannot see color at all.
2. You can make links a color which is very different from the surrounding text (a 3:1 ratio), 
   AND ensure that when the link is selected with the keyboard or mouse that it appears   
   differently from regular text without relying on color alone.

Unless you have disabled the `outline` CSS style, links will automatically appear visually distinct
when selected with the keyboard.

link-contrast

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

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

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 (e.g., `<ul>` or `<ol>`) should only contain list items (`<li>`) as a direct descendant 
to ensure that screen readers can accurately report the amount of items contained in the list. 

## Example

In the following example, some screen readers would say this list has two items, instead of 
four: 

```html
<ul>
    <div class="some_class">
        <li>Example 1</li>
    </div>
    <div class="some_other_class">
        <li>Example 2</li>
        <li>Example 3</li>
        <li>Example 4</li>
    </div>
</ul>
```

To fix this, you would need to remove the `<div class="some_class">` and 
`<div class="some_other_class>` elements and ensure only `<li>` list items remain.

## Further reading

The [formal specification for the list element](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/ul)
shows what is and is not permitted inside an `<ul>` and `<ol>`.

See [Technique H88](https://www.w3.org/TR/WCAG20-TECHS/H88.html) for more information.

list-not-following-semantics

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

Images should specify appropriate
[alternative text](https://help.silktide.com/en/articles/8020957-alternative-text), 
where appropriate.

Alternative text is text that is used in place of an image if it cannot
be seen. This is important for users who are blind or partially sighted, 
who may have the page read to them by a screen-reader. Without alternative 
text, they will not know what the image is, or what it is for.

## How to fix this issue 

In most cases, you can fix this issue by adding alternative text to the media
in your Content Management System (CMS).

If you need to do this in code, you can alternative text to an image using 
the `alt` attribute. For example: 

```html
<img src="apple.png" alt="A red 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.

It is not always appropriate to provide alternative text. For example, if an
image is purely decorative - it adds nothing to the content of the page - then
it is better to omit the alternative text entirely. This is because screen-reader
users will have to listen to the alternative text, which can be annoying if it
is not useful, or highly repetitive.

To specify that an image is decorative, use an empty `alt` attribute, e.g.:

```html
<img src="decorative-image.png" alt="">
```

## Methodology

This check tests if the `alt` attribute is present on an image. If it is not, 
then the check fails.

Some images are excluded from this check:

1. **Images without a `src` attribute.** This is because they are
   not visible to users, and therefore do not need alternative text.
2. **Images which are 1px in width or height.** This is because they are only
   used for tracking pixels, or (rarely) layout purposes, and do not need 
   alternative text.
3. **Images which are hidden from screen readers using the `aria-hidden` attribute.**
   This is because they are not accessible to screen readers, and therefore would not 
   use their alternative text.

## More information

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

Form controls must appear sufficiently distinct from their surroundings, so that people 
with visual impairments are still able to clearly see them.    

Either the border or the form control itself must have a 3:1 colour contrast with the 
surrounding area. 

## Methodology

* All `<input>`, `<textarea>`, and `<select>` elements are checked.
* For `<input>` elements, these types are ignored as their
  appearance is controlled by the browser or operating system:
  `checkbox`, `radio`, `submit`, `reset`, `image`, `hidden`, `file`. 
* The flattened background color of the control is determined. This is the color of the
  control itself, combined with any parent elements if the control is transparent.
* If the control has a border or outline:
  * The flattened background color of each edge is determined. 
    This is the color of the edge itself, combined with any parent elements
    if the edge is transparent.
  * If any edge has sufficient contrast with the flattened background color of the control, 
    the control is considered to have sufficient contrast.
* If the control does not have a border or outline:
  * The flattened background color of the surrounding 
    area is determined. This is the color of the first control's parent element which is at least 
    one pixel larger around the element in every dimension, i.e. above, below, left, and right.
  * If the background color of the element has sufficient contrast with surrounding area color
    the control is considered to have sufficient contrast.

## Troubleshooting

There are some limitations to the contrast checker:

* The use of drop shadows, glowing effects, gradients, and other complex effects 
  mean there is no one clear color to determine the contrast ratio against. 
  In these cases, the contrast ratio cannot currently be determined.
* It is possible for an element to be positioned over multiple elements, e.g. via
  `position: absolute` or `position: fixed`. In this case, the contrast ratio cannot 
  currently be determined.

## Further reading

* [WCAG 1.4.11](https://www.w3.org/WAI/WCAG21/Understanding/non-text-contrast.html)

non-text-contrast

Ensure the first heading in PDF documents is marked as Heading Level 1 (H1) for accessibility.

## What this means

In a well-structured PDF, the very first heading should be a Heading 1 (H1), which typically represents the main title or the most important heading in the document. This is similar to the primary heading on a webpage, setting the context for the content that follows.

## Why it matters

1. **Accessibility**: For screen reader users, an H1 heading is the primary entry point to understand what the document is about. It's crucial for navigating and comprehending the content.
2. **Document Structure**: The H1 heading sets the stage for the document's structure, much like a book's title. It helps in organizing the content logically.
3. **Search Engine Optimization**: For documents available online, having a clear H1 heading can aid in search engine recognition and ranking.

## How to fix

1. **Review Your Document**: Open your PDF and check the first heading. It should be marked as H1, clearly indicating the main topic or title of the document.
2. **Edit if Necessary**: If the first heading is not H1, use a PDF editing tool to change the heading level. Ensure that it is prominently styled and stands out as the main title.
3. **Maintain Hierarchy**: After setting the H1, ensure that subsequent headings follow in a logical hierarchical order (H2, H3, etc.).

## Testing Methodology

Silktide's identifies the first heading (if any) and verifies 
if it is correctly marked as H1.

### Limitations
- **Styling vs. Tagging**: Silktide detects headings based on tagging, not styling. A visually prominent heading might not be detected as H1 if not tagged correctly.
- **Document Variations**: In some documents, like research papers, the first heading might not be the main title. Silktide's check assumes standard document formatting.

## Further Reading

- [PDF9: Providing headings by marking content with heading tags in PDF documents](https://www.w3.org/TR/WCAG20-TECHS/pdf.html#PDF9)
- [PDF Accessibility - Headings](https://www.adobe.com/accessibility/pdf/pdf-accessibility-overview.html)
- [WCAG Guidelines on Headings](https://www.w3.org/TR/WCAG21/#headings-and-labels)

pdf-headings-h1-first

Ensures that headings in PDF documents follow a logical hierarchical order for accessibility.

## What this means

Headings in a PDF should be arranged in a logical sequence, much like a table of contents in a book. This means using a consistent hierarchy of heading levels (like Heading 1 for main titles, Heading 2 for subsections, etc.). Headings should not skip levels abruptly (e.g., jumping from Heading 1 directly to Heading 3).

## Why it matters

1. **Accessibility**: Screen readers rely on a logical heading structure to navigate content, making it essential for users with visual impairments.
2. **Readability and Navigation**: A well-structured document with logically ordered headings enhances readability and allows all users to navigate the content more efficiently.
3. **Consistency and Professionalism**: Logical heading order reflects a professional approach to document creation and helps maintain consistency across documents.

## How to fix

1. **Review Heading Levels**: Check your document to ensure that headings follow a sequential order without skipping levels.
2. **Modify Headings**: If any headings are out of order, adjust them using your PDF editing tool to align with the logical structure.

## Testing Methodology

Silktide's checks your PDF to identify the sequence of headings. It flags PDFs where the heading order is not 
hierarchical (e.g., a Heading 3 directly following a Heading 1).

Headings in a PDF should follow the sequence Heading 1 > Heading 2 > Heading 3 without skipping intermediate headings.
It is acceptable to 'go back' to previous styles/headings but the sequence should then continue without missing headings.

### Limitations
- **Contextual Analysis**: Silktide might not fully grasp the context behind the document's structure, so manual review is recommended for complex documents.
- **Styling Variations**: Variations in styling that are not properly tagged might not be detected accurately.

## Further Reading

- [Understanding WCAG: Headings and Labels](https://www.w3.org/WAI/WCAG21/Understanding/headings-and-labels.html)
- [How to Organize PDF Content with Accessible Headings](https://www.adobe.com/accessibility/pdf/pdf-accessibility-overview.html)

pdf-headings-order

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)

pdf-no-title

Webpages should provide a way to skip to the main content of the page. There are 
several ways to accomplish this.

The most common solution is a "Skip to content" link:

```html
<a href="#main">Skip to main content</a>
...
<div id="main">
<h1>Welcome to this page</h1>
```

This link is usually hidden from users unless selected, so it doesn't need to compromise the look of 
your page.

Alternatively, you can use the `<main>` HTML landmark:

```html
<main>
<h1>Welcome to this page</h1>
``` 

or an ARIA role of `main`:

```html
<div role="main">
<h1>Welcome to this page</h1>
``` 

Generally best practice is to combine these approaches, using `<main>` landmark with a link pointing to it:

```html
<a href="#main">Skip to main content</a>
...
<main id="main">
<h1>Welcome to this page</h1>
```

This approach will be most widely supported by screen readers and understood by the highest number of users.

# 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.

Most web pages have a header containing branding and navigation on every page. Stepping through 
this repetitive part of the page can be hugely frustrating for users of assistive technology. For example, 
a blind user may have to listen to hundreds of navigation links before they can reach the content on a page.

Adding a means to skip directly to the page content massively enhances the experience for these users.

Skip to content links do not need to be visible to everyone. A common implementation means they are only 
experienced by users via the tab key or other assistive technology 
(see [skipping to navigation links](https://webaim.org/techniques/skipnav/) from WebAIM). 

# Methodology

It is not sufficient to include a "skip to content" link. The link must work, and it must appear early
enough in the page to be useful.

* If the page has less than 500 visible characters, it does not require a "skip to content" link.
* If the page has a main landmark (e.g. `<main>` or `role="main"`) it does not require a "skip to content" link.
* Silktide looks for a link with a fragment (e.g. `#main`) pointing to a lower part of the page. The link 
  must not be adjacent to other text nodes. 
* The fragment must point to an ID that exists, or this check will raise an error.
* The link must appear before 500 visible characters of text in the page, or this check will raise an error.

The text inside the link is not considered, as this test must support a wide range of languages.

# Learn more

More about [skipping to navigation links](https://webaim.org/techniques/skipnav/) from WebAIM and 
see [W3C's recommended technique](https://www.w3.org/TR/2016/NOTE-WCAG20-TECHS-20161007/G1).

skip-to-content

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.

two-dimensional-scrolling

wcag-22.score

wcag-22-a.score

wcag-22-aa.score

wcag-22-aaa.score

website.pages

website.documents

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

## Requirements
WCAG requires that captions:

* Represent all spoken dialogue
* Indicate who is speaking, when not visually obvious
* Include important non-speech sounds, like:
  * Laughter
  * Alarms
  * Music lyrics or tone (if meaningful)
  * Sound cues (e.g. _door creaks_)

## What this check looks for

This check identifies video and audio on the page, and checks whether that includes machine-readable captions.

This check will fail if:

* There is a video or audio element that is not muted, and it does not contain a caption track.
* There is a link to a known video platform (such as Vimeo) where captions are not clearly available.

## How this check works

### 1. Videos or audio using HTML5

The check scans for `<video>` and `<audio>` elements directly in the page’s HTML. For each one, it looks at:

* **Whether the media is muted**
  If the media is permanently muted using the muted attribute, the check ignores it. Muted media is assumed not to convey important information through audio.
* **Whether captions are provided**
  The check looks for a <track> element inside the media tag, which is where captions should be included. If no caption track is found, the media fails this check.

Only the first video file source is reported for each video, to avoid confusion from fallback formats.

### 2. Links to external video players

The check also looks for links to known video platforms such as Vimeo. If a link appears to go directly to a video 
and there’s no indication that captions are available, the check flags it.

## When captions aren’t needed

If the media is silent, decorative, or doesn’t include any meaningful audio content, then captions may not be 
necessary. However, in most cases where information is conveyed through audio, captions must be provided to 
meet accessibility requirements.

## Further reading

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

prerecorded-captions-alternative

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

When an image is the only content of a link, it should specify alternative text, 
via an `alt` attribute. The alternative text should describe the purpose of the link.

Without this, some users will be unable to determine what a link does, for example anyone 
using a screen reader.

To fix this, simply add an `alt` attribute to the image inside the link, e.g.:

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

Priority	Recommendation	Progress
	Allow users to quickly skip to content WCAG 2.0 A 2.4.1	24%
	Ensure pages don't scroll in two dimensions on small screens WCAG 2.1 AA 1.4.10	54.1%
	Ensure links are distinguished by more than just color WCAG 2.0 A 1.4.1	32%
	Ensure PDFs have a title WCAG 2.0 A 2.4.2	28.5%
	Ensure lists are marked up correctly WCAG 2.0 A 4.1.1	52%

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