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But there is a crucial difference: the two halves work in complementary ways. If you left-click on the right-hand half of the icon, you get a list of tags; if you left-click on the left-hand half of the icon you get a box into which you enter a tag name. But IME it is easy to left-click the wrong half by mistake – opening the entry box, when you really intended to click on the right half to unfurl the list.