I don't think it's necessiary to import plugins to qml now.

Turn to another demo instead.
come to "Extending QML".
"Extending QML" step 2 and 3
"Extending QML" step 4 to step 7

both "Attached Properties" and "Grouped Properties" can't be auto
completed in Qt Creator, I don't feel like this...

Maybe Qt5.2 is worth waiting for, oh, just maybe.