Thanks, But this part I understood, it is the comparison with qr that I am puzzeled about.

/o and qr// provide different services to the programmer:

/o says 'Take this pattern and create a compiled regex that will not change for the life of the program'

qr// says 'Take this pattern and return a special object that I can assign to a variable, interpolate into another pattern, pass to a subroutine, etc, etc, and as a side-effect creates a compiled form that I can use in pattern matches directly.'