title: What do these signals mean: activated, entered, pressed, viewportEntered?
body: <p>I see these signals in <strong>PySide2.QtWidgets.QAbstractItemView</strong>, some of which are easy to understand, such as <strong>clicked</strong>, <strong>doubleClicked</strong>. For some, the meaning cannot be determined, such as <strong>activated</strong>, <strong>entered</strong>, <strong>pressed</strong>, <strong>viewportEntered</strong>. These signals are also not explained in the manual:<a href="https://doc.qt.io/qtforpython-5/PySide2/QtWidgets/QAbstractItemView.html#PySide2.QtWidgets.PySide2.QtWidgets.QAbstractItemView.activated" rel="nofollow noreferrer">https://doc.qt.io/qtforpython-5/PySide2/QtWidgets/QAbstractItemView.html#PySide2.QtWidgets.PySide2.QtWidgets.QAbstractItemView.activated</a></p>
  <p>In fact, I want to emit a signal when <strong>QTreeView.currentIndex</strong> changes. I used <strong>clicked</strong> before, but when I use the keyboard up and down arrows to select items, <strong>clicked</strong> doesn't work.</p>