A prompt element controls the output of pre-recorded audio and synthesized speech. It allows for both forms of audio output to be combined or, in some cases, for using the synthesized speech as an alternative when pre-recorded audio is not available.
This section will cover the different ways to output audio and will also highlight some of the differences between the VoiceXML 2.0 Draft and the VoiceXML 1.0 Specification.
Though prompt is used to control audio and speech output, it is not always necessary to explicitly use the <prompt> and </prompt> tags. The prompt tags are needed only when:
speech markup elements are used,
audio and synthesized speech are interleaved, or
any attributes ...