Barker Library - TP248.2.E83 2019

Online Resource

Over the weekend two new HTML5 elements – summary and figcaption – were added to the draft specification. The introduction of summary and figcaption marks the acceptance that new elements are needed to act as captions or legends for the details and figure elements. The addition of the figcaption element finally begins to clear up the difficulty in marking-up figure element captions and looks to cement the place of the figure element in the HTML5 specification. The summary element does much the same for the details element but the very nature of the details element itself means that its future is not yet clear.

The figcaption element

This new element acts as the optional caption or legend for any content contained within its parent figure element.

If there is no figcaption element within a figure element then there is no caption for the rest of its content. If there is a figcaption element then it must be the first or last child of the figure element and only the first figcaption element (should there be more than one child figcaption of the parent figure element) represents a caption.

The figure element is used to mark up any self-contained content that may be referenced from the main flow of a document but could also be removed from the primary content (for example, to an appendix) without affecting its flow. This makes it suitable for various types of content ranging from graphs and data tables to photographs and code blocks.

<p><a href="#fig-ftse">Figure 1</a> shows the extent of the collapse in the markets and how recovery has been slow.</p>

<figure id="fig-ftse">
  <figcaption>Figure 1. The value of the FTSE 100 Index from 1999&ndash;2009.</figcaption>
  <img src="ftse-100-index-graph.jpg" alt="The index hit a record high at the end of 1999 and experienced two significant drops in the following last decade.">
</figure>

<p>This latest financial crisis hasn't stopped Alex from writing music and his latest track is actually worth listening to.</p>

<figure>
  <audio src="what-am-i-doing.mp3" controls></audio>
  <figcaption><cite>What am I doing?</cite> by Alex Brown</figcaption>
</figure>

The creation of the figcaption element is an important step forward for the HTML5 draft specification as it finally provides a reliable means to markup the caption for content that is best marked up as a figure. Previous attempts to use the legend element, the caption element, and the dt and dd elements had failed due to a lack of backwards compatibility when it came to styling these elements with CSS.

The summary element

This new element represents a summary, caption, or legend for any content contained within its parent details element.

The summary element must be the first child of a details element and if there is no summary element present then the user agent should provide its own. The reason for this is because the details element has a specific function – to markup additional information and allow the user to toggle the visibility of the additional information. Although it is not specified in the specification, it is expected that the summary element will act as the control that toggles the open-closed status of the contents of the parent details element.

<details>
  <summary>Technical details.</summary>
  <dl>
    <dt>Bit rate:</dt> <dd>190KB/s</dd>
    <dt>Filename:</dt> <dd>drum-and-bass-mix.mp3</dd>
    <dt>Duration:</dt> <dd>01:02:34</dd>
    <dt>File size:</dt> <dd>78.9MB</dd>
  </dl>
</details>

The introduction of the summary element seems to secure the future of the details element and the new behaviour that it affords, for now. When user agents begin to add support for the details element you won’t need JavaScript, or even CSS, to have expanding or collapsing sections in an HTML document.

The future of the details element

There will continue to be some debate over the inclusion of behaviour in an HTML specification especially given the widespread use of JavaScript to provide the expand-collapse functionality that details describes.

The details element writes some quite significant behaviour into an HTML document and I can see it being abused to provide generic expand-collapse functionality throughout a document. It is also not entirely clear what purpose the details element actually serves other than being an attempt to bypass the need for JavaScript or CSS to expand or collapse sections of a document.

There has been a general softening of the rough distinction between content, presentation, and behaviour. JavaScript libraries are being used to patch holes in browser CSS and HTML5 support, the CSS3 modules introduce plenty of behaviour that was previously only possibly with JavaScript, and the HTML5 specification is also introducing functionality and behaviour that previously required the use of JavaScript.

The future survival of the details element, and the behaviour associated with it, may well depend on browser implementations and author applications over the coming months.

What is the cascade?

The cascade is a mechanism for determining which styles should be applied to a given element, based on the rules that have cascaded down from various sources.

The cascade takes importance, origin, specificity, and source order of style rules into account. It assigns a weight to each rule. When multiple rules apply to a given element, the rule with the greatest weight takes precedence. The result is an unambiguous way to determine the value of a given element/property combination.

Browsers apply the following sorting logic:

• Find all declarations that apply to a given element/property combination, for the target media type.

• Sort declarations according to their importance (normal or important) and origin (author, user, or user agent). From highest to lowest precedence:

  1. user !important declarations
     
  2. author !important declarations
     
  3. author normal declarations
     
  4. user normal declarations
     
  5. user agent declarations

• If declarations have the same importance and source, sort them by selector specificity.

• Finally, if declarations have the same importance, source, and specificity, sort them by the order they are specified in the CSS. The last declaration wins.

What is specificity?

Specificity is a method of conflict resolution within the cascade.

Specificity is calculated in a very particular way, based on the values of 4 distinct categories. For explanatory purposes, the CSS2 spec represents these categories using the letters a, b, c, and d. Each has a value of 0 by default.

• a is equal to 1 if the declaration comes from a style attribute in the HTML (“inline styles”) rather than a CSS rule with a selector.
• b is equal to the number of ID attributes in a selector.
• c is equal to the number of other attributes and pseudo-classes in a selector.
• d is equal to the number of elements and pseudo-elements in a selector.

The specificity is given by concatenating all 4 resulting numbers. More specific selectors take precedence over less specific ones.

For example, the selector #id .class[href] element:hover contains:

• 1 ID (b is 1)
• 1 class, 1 attribute selector, and 1 pseudo-class (c is 3)
• 1 element (d is 1)

Therefore, it has a specificity of 0,1,3,1. Note that a selector containing a single ID (0,1,0,0) will have a higher specificity than one containing any number of other attributes or elements (e.g., 0,0,10,20). This is one of the reasons why many modern CSS architectural patterns avoid using IDs for styling purposes.

What is inheritance?

Inheritance is distinct from the cascade and involves the DOM tree.

Inheritance is the process by which elements inherit the the values of properties from their ancestors in the DOM tree. Some properties, e.g. color, are automatically inherited by the children of the element to which they are applied. Each property defines whether it will be automatically inherited.

The inherit value can be set for any property and will force a given element to inherit its parent element’s property value, even if the property is not normally inherited.

About !important

The above should make it apparent that !important is a separate concept to specificity. It has no effect on the specificity of a rule’s selector.

An !important declaration has a greater precedence than a normal declaration (see the previously mentioned cascade sorting logic), even declarations contained in an element’s style attribute.

[CSS terminology reference]

Translations

• CSS: каскад, специфика и наследование

‘U.P. government crushing their rights’

McGinn, Jeffrey

The Minister also asked the States to ensure adoption of infection, prevention and control (IPC) practices in all health-care settings to avoid and reduce chances of infections to health-care workers.

Lately I've been using variables to plan out pure CSS timelines for complex animations. I built an SVG and CSS Rube Goldberg machine to put this technique to the test!

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Online Resource

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