[io grant] Straighten up copy, move, rename

- Shorten and unify prose
- List new type constraints as implemented in
    rakudo/rakudo@ff97083419

Author: zoffixznet

doc/Type/IO/Path.pod6

@@ -581,42 +581,37 @@ number (or string containing a decimal number):
 
 =head2 routine rename
 
-    method rename(IO::Path:D: $to, :$createonly --> Bool)
-    sub    rename($from, $to, :$createonly --> Bool)
+    method rename(IO::Path:D: IO() $to, :$createonly = False --> Bool:D)
+    sub    rename(IO() $from, IO() $to, :$createonly = False --> Bool:D)
 
-Renames a file. Both C<$from> (the file to be renamed) and C<$to> (the
-destination) can take arbitrary paths. If C<:createonly> is set to C<True>,
-the rename fails if a file already exists in the destination.  Returns
-C<True> upon success, or L<fails|/routine/fail> with L<X::IO::Rename> if the
-operation could not be completed.
+Renames a file or directory. Returns C<True> on success; L<fails|/routine/fail>
+with L<X::IO::Rename> if C<:$createonly> is C<True> and the C<$to> path already
+exists or if the operation failed for some other reason.
 
-Please use L<move|/routine/move> if a file could not be moved by renaming
-(usually because the destination is on a different physical storage device).
+B<Note:> some renames will always fail, such as when the new name is on a
+different storage device. See also: L«C<move>|/routine/move».
 
 =head2 routine copy
 
-    method copy(IO::Path:D: $to, :$createonly)
-    sub    copy($from, $to, :$createonly)
+    method copy(IO::Path:D: IO() $to, :$createonly --> Bool:D)
+    sub    copy(IO() $from, IO() $to, :$createonly --> Bool:D)
 
-Copies a file, as indicated by C<$from> or the invocant, to the
-destination specified.  If C<:createonly> is set to C<True>, copy fails if a file
-already exists in the destination.  Returns C<True> upon success, or an
-appropriate C<Failure> if the operation could not be completed.
+Copies a file. Returns C<True> on success; L<fails|/routine/fail>
+with L<X::IO::Rename> if C<:$createonly> is C<True> and the C<$to> path already
+exists or if the operation failed for some other reason.
 
 =head2 routine move
 
-    method move(IO::Path:D: $to, :$createonly)
-    sub    move($from, $to, :$createonly)
+    method move(IO::Path:D: IO() $to, :$createonly --> Bool:D)
+    sub    move(IO() $from, IO() $to, :$createonly --> Bool:D)
 
-Moves a file. Both C<$from> (the file to be moved) and C<$to> (the
-destination) can take arbitrary paths. If C<:createonly> is set to C<True>,
-the move fails if a file already exists in the destination.  Returns C<True>
-upon success, or L<fails|/routine/fail> with L<X::IO::Move> if the operation
-could not be completed.
+Copies a file and then removes the original. If removal fails, it's possible
+to end up with two copies of the file. Returns C<True> on success;
+L<fails|/routine/fail> with L<X::IO::Rename> if C<:$createonly> is C<True> and
+the C<$to> path already exists or if the operation failed for some other reason.
 
-Please use L<rename|/routine/rename> if a file can be moved by renaming
-(which is usually possible if the destination is on the same different
-physical storage device).
+To avoid copying, you can use L«C<rename>|/routine/rename», if the files are on
+the same storage device. It also works with directories, while C<move> does not.
 
 =head2 routine symlink