platform.window:width is a function that is part of platform.window.
This has been introduced in TI-Nspire OS 3.0 (Changes).
Returns the width in pixel of the current display window.
Below is an example of a program that creates/updates the "theHeight" and "theWidth" global variables whenever the user resizes the widget's frame:
function on.resize() --Define a function for the event theWidth = platform.window:width() theHeight = platform.window:height() end