The text nested within this element will be replaced by the value specified within the alias attribute. Do note that SSML tags are ignored by some of the available TTS engines, while some engines use their own non-compliant markup. Check the Text-To-Speech appendices for additional details.
usage
<sub alias="CDATA">
attributes
alias
Data Type: CDATA
Default: Required
The alias attribute denotes the substitute text to be rendered in place of the content nested within the phoneme element.