12. One or more computing devices, comprising: a processor; and storage storing computer-executable instructions which, when executed by the processor, cause the processor to: receive a message provided by a particular user; determine whether the message provided by the particular user includes a selection control command specifying a target media item to be played by media playback equipment, or a non-selection control command; where the message is determined to contain the selection control command: send the message as an input query to a search system, with instruction that the search system is to perform a domain-specific search, receive a query response to the input query from the search system, the query response identifying a top-ranked media item that corresponds to the target media item, and control the media playback equipment to play the top-ranked media item; and where the message is determined to contain the non-selection control command, control the media playback equipment based at least on the non-selection control without interacting with the search system.
12. One or more computing devices, comprising: a processor; and storage storing computer-executable instructions which, when executed by the processor, cause the processor to: receive a message provided by a particular user; determine whether the message provided by the particular user includes a selection control command specifying a target media item to be played by media playback equipment, or a non-selection control command; where the message is determined to contain the selection control command: send the message as an input query to a search system, with instruction that the search system is to perform a domain-specific search, receive a query response to the input query from the search system, the query response identifying a top-ranked media item that corresponds to the target media item, and control the media playback equipment to play the top-ranked media item; and where the message is determined to contain the non-selection control command, control the media playback equipment based at least on the non-selection control without interacting with the search system. 13. The one or more computing devices of claim 12 , wherein the computer-executable instructions further cause the processor to: provide one or more instances of a collaborative user interface presentation for use by respective users in a group of users, including the particular user.