Comment 4 for bug 1557802

Yeah, that is too old.
The sensingArea property was added in revision 1866
http://bazaar.launchpad.net/~ubuntu-sdk-team/ubuntu-ui-toolkit/staging/revision/1866
while your phone is running version 1795

Please note that the -dev documentation is generated from the packages available in the rc-proposed channel, so you have to run the latest OS on rc-proposed channel to make sure you get the UITK version that the -dev documentation refers to.