Client-specific data
Type information in the Client-specific data box to designate a text string that chat client developers can use to pass instructions or parameters to custom clients. This string is limited to 255 ANSI or Unicode characters.

You can also use this string to send a client's Globally Unique Identifier (GUID), which represents an ActiveX control that runs on the client. A GUID is a unique number that identifies a Dynamic Link Library (DLL) file. The GUID is generated when the DLL is registered. An example of a GUID is {F1CC3C17-09E3-11d1-873D-00C04FB6E8E9}.