Comments

; comment
(some more comments)
G28 (even in here) X0

Quoted strings

"foo""bar"

Full example

M190 S60 ; Heat bed to 60°C
G21 ; Set units to millimeters
G28 ; Move to Origin (Homing)
G29 ; Auto Bed Leveling
G28 X0 Y0 ; Home X and Y to min endstops
M107 ; Fan off
M109 S200 ; Heat hotend to 200°C
G92 E0 ; Set current extruder position as zero
G1 F200 E15 ; Extrude 15mm filament with 200mm/min
G92 E0 ; Set current extruder position as zero
G1 F500