As for this problem, the most probable and the most likely answer for this one would be DELETE.
One way to delete a note is to tap or click immediately to the left of the note reference mark in the document text and then press the delete key twice. Other keys exhibit the same results when used differently and some do not exhibit as expected. This solely depends as to when it was used or as to what it was used for. Usually there are shortcuts and other things that complicate the usage of keys, but they sure pave way for us users to be more comfortable at our own pace.