There are several concepts of HTML that apply in the voice world. For example, the document structure itself defines an implicit sequential flow of control. By reusing HTML as much as possible, we make VXML easier to learn and easier to use. Converting text to audio output is a challenging problem. In principle, we agree that specific speech markup is the correct solution to minimizing the ambiguity inherent in text.
Similar work is underway for other specialized markup such as Automatic Speech Recognition grammars.
Such formalisms are outside the scope of the VXML definition, but a method for their incorporation should be identified. Conclusion Given the huge volume of information published through HTML, and the range of services that are evolving on the Web, it is attractive to offer a voice interpretation of HTML content. We believe that work can and will progress in this area, but that there will be a desire on the part of many content providers to target the voice medium precisely and directly, to create high-quality voice services. Since it seems to us that HTML, even with extensive style embellishment, is incapable of specifying the details of the necessary voice interactions, our preference would be to standardize on a fully explicit voice interaction language. This language could in turn be targeted by applications that form a continuum from voice browsing of existing HTML to hosting of IVR services.