There should be a ? button in the button row next to the tabs. When clicking it, it should show a pressed-down state and turn the cursor into a question mark. The next thing the user clicks on then is the item the user wants to know more about. PV should then show a help text describing what the item is and what it does.
This should be useful esp. for touch devices where tooltips don't work and users can't be expected to intuitively guess the function of all buttons.
To save screen space for advanced users, this button should be hideable from the settings dialog.
Note to self: http://doc.qt.io/qt-4.8/qwhatsthis.html#details