GNOME provides support for accessibility devices using the ATK framework. This framework defines a set of interfaces to which graphical interface components adhere. This allows, for instance, screen readers to read the text of an interface and interact with its controls. ATK support is built into GTK+ and the rest of the GNOME platform, so any application using GTK+ will have reasonable accessibility support for free.
Nonetheless, you should be aware of accessibility issues when when developing your applications. Although GTK+ interfaces provide reasonable accessibility by default, you can often improve how well your program behaves with accessibility tools by providing additional information to ATK. If you develop custom widgets, you should ensure that they expose their properties to ATK