10 REM The ZX Spectrum display is 32 columns wide, so we have 8 columns of 4 spaces
20 FOR r=0 TO 20: REM There are 21 rows
30 FOR c=0 TO 7: REM We use the native colour sequence here
40 PAPER c: REM set the background colour for the spaces to be printed
50 PRINT "    ";: REM four spaces, the semicolon prevents newline
60 NEXT c
70 REM at this point the cursor has wrapped, so we don't need a newline
80 NEXT r