"+p seem to behave the same.
:help "*, but it's talking about mouse selection, and
:help "+ tells me
There are three documented X selections: PRIMARY (which is expected to represent the current visual selection - as in Vim's Visual mode), SECONDARY (which is ill-defined) and CLIPBOARD (which is expected to be used for cut, copy and paste operations).
Of these three, Vim uses PRIMARY when reading and writing the
"*register (hence when the X11 selections are available, Vim sets a default value for 'clipboard' of "autoselect"), and CLIPBOARD when reading and writing the
"+register. Vim does not access the SECONDARY selection.
But I don't understand this; what's it got to do with visual mode? What are X selections?