




 
A pointer to an Objective-C foreign object.
A selector of type 
sel
.
A string or 
nil
.
A pointer to an Objective-C foreign object or 
nil
.
A notification center.
The function 
add-observer
 calls the Objective-C instance method 
"addObserver:selector:name:object:"
 of 
centre
 to add 
target
 as an observer for 
selector
 with the given 
name
 and 
object
, which both default to 
nil
.
If center is omitted then it defaults to the default notification center.