Synopsis:
   $winbound(<channel name>/<window name>/<window refnum>)

Technical:
   If the first argument refers to a channel, the function returns the window
   refnum that the channel is bound to (if any). If the argument refers to
   a window, the channel bound to that window is returned (if any).

Practical:
   This can be used to determine wether a channel is already bound, as to not
   bind it twice.

Returns:
   channel name, if argument refers to a window
   window refnum, if argument is a channel
   nothing, if channel/window is not bound

Examples:
   /window refnum 2 bind #epic
   eval echo $winbound(2)                           /* returns "#epic" */
   eval echo $winbound(#epic)                       /* returns 2 */

Other Notes:
   If a given window name looks like a channel, the window name takes
   precedence.