The Texture Address variable can be used to define the area that the NineSlice displays. By default the Texture Address is set to Entire Texture which means the NineSlice will display the entire source file (split up among the nine pieces.
The Custom value allows specifying a custom set of coordinates for the Nine Slice. Custom is most often used to when an image is part of a sprite sheet. For example, the following image shows a NineSlice using a portion of a texture. The NineSlice uses the following variables:
The Sprite next to the NineSlice displays the entire texture.