13.3 Saving Rectangles in Registers
A register can contain a rectangle instead of linear text. See Rectangles, for basic information on how to specify a rectangle in the buffer.
C-x r r r
Copy the region-rectangle into register r
( copy-rectangle-to-register). With prefix argument, delete it as
well.
C-x r i r
Insert the rectangle stored in register r (if it contains a
rectangle) ( insert-register).
The C-x r i r ( insert-register) command,
previously documented in Saving Text in Registers, inserts a rectangle
rather than a text string, if the register contains a rectangle.