vim-patch:9.1.0155: can only get getregion() from current buffer (#27757)

Problem:  can only call getregion() for current buffer
Solution: Allow to retrieve selections from different buffers
          (Shougo Matsushita)

closes: vim/vim#14131

84bf6e658d

Co-authored-by: Shougo Matsushita <Shougo.Matsu@gmail.com>

runtime/lua/vim/_meta/vimfn.lua

@@ -3525,11 +3525,13 @@ function vim.fn.getreg(regname, list) end
 --- @return table
 function vim.fn.getreginfo(regname) end
 
---- Returns the list of strings from {pos1} to {pos2} in current
+--- Returns the list of strings from {pos1} to {pos2} from a
 --- buffer.
 ---
 --- {pos1} and {pos2} must both be |List|s with four numbers.
---- See |getpos()| for the format of the list.
+--- See |getpos()| for the format of the list.  It's possible
+--- to specify positions from a different buffer, but please
+--- note the limitations at |getregion-notes|
 ---
 --- The optional argument {opts} is a Dict and supports the
 --- following items:
@@ -3550,6 +3552,7 @@ function vim.fn.getreginfo(regname) end
 --- This function is useful to get text starting and ending in
 --- different columns, such as a |charwise-visual| selection.
 ---
+---           *getregion-notes*
 --- Note that:
 --- - Order of {pos1} and {pos2} doesn't matter, it will always
 ---   return content from the upper left position to the lower
@@ -3559,8 +3562,12 @@ function vim.fn.getreginfo(regname) end
 --- - If the region is blockwise and it starts or ends in the
 ---   middle of a multi-cell character, it is not included but
 ---   its selected part is substituted with spaces.
---- - If {pos1} or {pos2} is not current in the buffer, an empty
+--- - If {pos1} and {pos2} are not in the same buffer, an empty
 ---   list is returned.
+--- - {pos1} and {pos2} must belong to a |bufloaded()| buffer.
+--- - It is evaluated in current window context, this makes a
+---   different if a buffer is displayed in a different window and
+---   'virtualedit' or 'list' is set
 ---
 --- Examples: >
 ---   :xnoremap <CR>