21. The non-transitory computer-readable storage medium of claim 15 , wherein the dynamic grammar is derived for use in processing second user input received after receiving the user speech input.
21. The non-transitory computer-readable storage medium of claim 15 , wherein the dynamic grammar is derived for use in processing second user input received after receiving the user speech input. 22. The non-transitory computer-readable storage medium of claim 21 , the instructions further comprising: after deriving the dynamic grammar, presenting a prompt to the user to obtain the second user input; and processing the second user input with the dynamic grammar to identify a desired selection identifier from the plurality of selection identifiers.