CSS rest-before

The CSS rest-before property is used in speech media to specify a prosodic boundary (silence with a specific duration) before an element.

A prosodic boundary is defined as "silence with a specific duration". In other words, the rest-before property allows you to set a pause before an element. Prosodic boundaries are a normal part of spoken language, and they can be a crucial part of helping the listener comprehend the words and meaning of the spoken text.

The rest-before property can be seen as the speech media equivalent to the padding-top property in visual media.

Also see rest and rest-before.


Possible Values

Expresses the rest in absolute time units (for example 50ms). Only non-negative values are allowed.
Equivalent to 0ms (no prosodic break is produced by the speech processor).
x-weak, weak, medium, strong, and x-strong
These values express the rest by the strength of the prosodic break in speech output. The exact time will depend on the output device/user agent being used.

In addition, all CSS properties also accept the following CSS-wide keyword values as the sole component of their property value:

Represents the value specified as the property's initial value.
Represents the computed value of the property on the element's parent.
This value acts as either inherit or initial, depending on whether the property is inherited or not. In other words, it sets all properties to their parent value if they are inheritable or to their initial value if not inheritable.

General Information

Initial Value
Applies To
All elements.

Example Code

Official Specifications

Vendor Prefixes

For maximum browser compatibility many web developers add browser-specific properties by using extensions such as -webkit- for Safari, Google Chrome, and Opera (newer versions), -ms- for Internet Explorer, -moz- for Firefox, -o- for older versions of Opera etc. As with any CSS property, if a browser doesn't support a proprietary extension, it will simply ignore it.

This practice is not recommended by the W3C, however in many cases, the only way you can test a property is to include the CSS extension that is compatible with your browser.

The major browser manufacturers generally strive to adhere to the W3C specifications, and when they support a non-prefixed property, they typically remove the prefixed version. Also, W3C advises vendors to remove their prefixes for properties that reach Candidate Recommendation status.

Many developers use Autoprefixer, which is a postprocessor for CSS. Autoprefixer automatically adds vendor prefixes to your CSS so that you don't need to. It also removes old, unnecessary prefixes from your CSS.

You can also use Autoprefixer with preprocessors such as Less and Sass.