This sample demonstrates a custom CommandHandler, AriaCommandHandler, that updates a DIV for screen reader accessibility.

This AriaCommandHandler adds more key commands for a user:

- Arrow keys: Change selection to a new node, if possible, based on direction. This is added to an internal navigation history.
- `B`: Give a description of which nodes are adjacent to the currently selected node
- `X`: Go backwards in the navigation history
- `C`: Go forwards in the navigation history

As these commands are executed, the AriaCommandHandler updates a DIV that has `aria-live="polite"` set with relevant text.

This is meant as a starting point to create a more individualized extention for your unique use case. Certain data and attributes of nodes that may be different between diagrams may be important to the accessibility interpretation.

### GoJS Features in this sample

#### GoJS Extensions

GoJS can be extended in a variety of ways. The most common way to change the standard behavior is to set properties on the GraphObject, Diagram, CommandHandler, Tool, or Layout. But when the desired property does not exist, you might need to override methods of CommandHandler, Tool, Layout, Link, or Node. Methods that you can override are documented in the API reference. Various features of GoJS can be overriden, either by replacing a method on an instance (a feature of JavaScript) or by defining a subclass. You should not modify the prototypes of any of the GoJS classes.

In addition to our samples, GoJS provides an extensions gallery, showcasing the creation of custom tools and layouts. Those classes and samples are written in TypeScript, available at `../extensionsJSM/`, as ECMAScript/JavaScript modules -- these use the `../release/go-module.js` library. We recommend that you copy the files that you need into your project, so that you can adjust how they refer to the GoJS library that you choose and so that you can include them into your own building and packaging procedures.

More information can be found in the GoJS Intro.

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