centerRect - "stretching" an image

[Sannyasin Brahmanathaswami]

See my other message to the list of UI Handlers…

For my library, I was looking for clues to "centering "  and came across 

centerRect

set the centerRect[angle] of image to rectangle
set the centerRect of image "buttonImage" to 20,20,45,200

Dictionary is obscure, 

1. What does "stretching" mean 
              in the context of " Use to centerRect property to specifies a region of pixels that should be stretched when the image is stretched." Something that happens is development with the Selection Tool on?

2.  centerRect[angle]
           Implies an array. But there is no reference to an array in the dictionary?

BR