How do I reassign the smartphone's shortcut buttons(the four buttons on the bottom (back, menu, home and search)) (Due to "We're sorry, but as a spam prevention mechanism, new users aren't allowed to post images.": http://www.letsgodigital.org/images/artikelen/1/android.jpg)
within my html5 webpage, so the user can search, go to the main page and open a website menu for faster access?
You cannot "reassign the smartphone's shortcut buttons" from within your "html5 webpage", unless this "html5 webpage" is running in some container with specific support for this (e.g., PhoneGap).
