[etc]

When a scale9Grid property is defined for a movie clip, the movie clip is divided into a grid with nine regions, based on the scale9Grid rectangle, which defines the center region of the grid.
You can think of the eight regions outside of the center (defined by the rectangle) as being like a picture frame that has special rules applied to it when the movie clip is scaled.

When the scale9Grid property is set and a movie clip is scaled, all text and child movie clips scale normally, regardless of which regions of the scale9 grid they are located in.