Indicates sections of a Web page that are particularly 'speakable' in the sense of being highlighted as being especially appropriate for text-to-speech conversion. Other sections of a page may also be usefully spoken in particular circumstances; the 'speakable' property serves to indicate the parts most likely to be generally useful for speech.
The *speakable* property can be repeated an arbitrary number of times, with three kinds of possible 'content-locator' values:
1.) *id-value* URL references - uses *id-value* of an element in the page being annotated. The simplest use of *speakable* has (potentially relative) URL values, referencing identified sections of the document concerned.
2.) CSS Selectors - addresses content in the annotated page, eg. via class attribute. Use the [cssSelector](http://schema.org/cssSelector) property.
3.) XPaths - addresses content via XPaths (assuming an XML view of the content). Use the [xpath](http://schema.org/xpath) property.
For more sophisticated markup of speakable sections beyond simple ID references, either CSS selectors or XPath expressions to pick out document section(s) as speakable. For thiswe define a supporting type, [SpeakableSpecification](http://schema.org/SpeakableSpecification) which is defined to be a possible value of the *speakable* property.
