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.

Syntax

Possible Values

time: Expresses the rest in absolute time units (for example 50ms). Only non-negative values are allowed.
none: 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:

initial: Represents the value specified as the property's initial value.
inherit: Represents the computed value of the property on the element's parent.
unset: 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: none
Applies To: All elements.
Inherited?: No
Media: Speech

Example Code

Official Specifications

CSS Speech Module (W3C Candidate Recommendation 20 March 2012)

"Pause" vs "Rest"

CSS3 includes "pause" properties and "rest" properties. Pauses are defined with the pause, pause-after, and pause-before properties. Rests are defined with rest, rest-before, and rest-after.

These "pause" and "rest" properties work in a similar way, however, they differ in where they're inserted.

The "pause" properties are placed outside of any cues that have been specified (i.e. using the cue, cue-before, or cue-after properties). So for example, any "pause before" is inserted between the preceding content and any "cue before". Likewise, any "pause after" is inserted between any "cue after" and the content that follows.

The "rest" properties are placed inside any cues. Therefore, a "rest before" will be inserted between any "cue before" and its subsequent content (and vice-versa for any "rest after").

CSS2

Note that in CSS2, the "pause" properties were placed inside any cues (like the CSS3 "rest" properties), however, this was changed in CSS3 to the placement mentioned above.

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.