Mobile device users must be able to zoom in and out consistently within applications on a mobile device. However the zooming actions may differ from one device model to another.
The product features and form factor of a mobile device determine which zooming actions application developers should make available on it:
If the device has an ITU-T keypad, the asterisk (*) key zooms in and the hash mark (#) key zooms out. This functionality is not available in editors or other states where the keys play another role. In these cases, the zoom functions, if applicable, must be available in the Options menu.
If the device has a QWERTY or half-QWERTY keyboard, use the two topmost keys at the top left of the keyboard for zooming in and out. For example, on a Latin keyboard, use the Q key to zoom in and the A key to zoom out. Some products might have zooming symbols printed on the keyboard to help users find the zooming features. Again, the functions are not available in editors.
On touch devices, users can use touch stripes to zoom. Finger movement along the stripe controls zooming. Applications may support different number of zoom levels. It should be possible to zoom across the full range with one swipe.
On touch devices with multiple touch support, users can use pinch zoom. See Multiple touch section for more details on pinch in and pinch out.
On touch devices, some applications may support double-tapping zoom. A double tap can toggle between zoomed and normal view, but this depends on the application.