The contents of a region are portrayed in the viewport only if they are within the region's window. Initially, the contents of the window are displayed at their full size in the region's viewport. A region's window is the only portion of the region that can be seen; the contents of a region that lie outside the region's window are not displayed in the viewport.

Once you have defined a textual region, the window size and/or position can be changed by specifying the change window size or the change window position action statements in a response definition or in an action routine definition. You can control what is visible in a region's window by changing the window's position or dimensions. As with a camera, if you zoom in, less of the area is visible through the lens. If you zoom out, more of the area is visible through the lens. Similarly, you control the part of the region that is visible on the screen by changing the size or the position of the window. You can:

•Reduce the window size to display less of the region (zoom in).

•Increase the window size to display more of the region (zoom out).

•Change the window position to display a different part of the region (pan).