Toggle page:
When you press this key, your hotbar will switch between Default and Toggle Page and remain there until you press this key again.

Switch to page (while holding):
When you press this key, your hotbar will switch to the Toggle Page. When you release it, it will return to the Default Page.

Use the blizzard keybindings frame to define the used toggle/switch keys and add a keybinding for the settings frame (where you can define which hotbars should be switched in the lower left bar).

Extras:
The addon will always change the hotbar to the Default Page on selecting a hostile target (except you press the shift key).

Credits:
Full Credit goes to Cladhaire for his great addon Page-on-Press (Standalone) and to Novan for his great addon PageSwitch.