bottomrow= see description
rightcolumn= see description
Clears an rectangular area with the space character.
rightcolumn default to their bottom-most/right-most valid values.
rightcolumn this sequence does nothing.
The colors of the cleared cells are not changed.
The other attributes of the cells are reset.
If filling the cells splits a multi cell character that character cleared, by replacing it by spaces, keeping its current attributes.
When only some of the lines have set set double width line, the region this sequence acts upon might not look rectangular in to the user on display.