Dear Mr,
I am very familiar with the NSTextField class. I used it extensively to allow runtime input and modification of object properties. This functionality laid the base for the scene editor I wrote for one of my past games. I created a subclass of NSTextField with some additional identification properties and callback functions. To complete your project, I would set the placeholder property of the subclassed TextField to "___.___.___.___". I would then override the insertText:replacementRange: function to add the additional behavior you desire, such as checking the validity of the format and moving the cursor to the next section when the correct number of digits has been specified or when the user enters a period or hits the space bar. To handle highlighting, I would use the setSelectedRange: function of the NSText class, which could be created from the NSString value of the NSTextField subclass.
Sincerely,
Ben