TopRow = 0 and LeftCol = 0 identify the top-left corner of the screen.

If a value greater than the maximum value is specified for TopRow, LeftCol, BotRow, RightCol, or Lines, the maximum value for that parameter is used.

If TopRow and LeftCol = 0, and if BotRow, RightCol, and Lines are greater than the screen lines, the entire screen is filled with the character-attribute pair defined by Cell.