set input_prompt [<string>]
This setting allows the user to add a custom string the the beginning of the input line (for display purposes). Much like the various Unix shells, the prompt can contain any string desired.
It is generally used for displaying information about the current target (such as a channel or queried nickname). Any variables used in the prompt are re-evaluated after each command issued from the input prompt.
Also note that any special highlight character (^B, ^C, etc) may be used in this setting.
To disable the input prompt, unset the variable.