G-code is a control language for the motors and laser diode of the machine, mostly given as raw coordinate data coupled with speed and power variables for the cutting.
G-code processing happens through an itermediary SVG export step, where an item is first exported into SVG, and the SVG file is broken down into series of coordinate points. The SVG step is not strictly necessary, but it allows rendering of a visualisation of the fabrication progress for the user to follow along.
Native SVG values are used to store all necessary cutting parameters: the stroke weight indicates laser head speed, opacity is equal to laser power, blue channel is the thickness of the material (in nanometers), and green channel the number of passes.
G-code export can alter some parameters automatically based on the used material. These include things like the thickenss of the fabric, the amount the material shrinks near the cut path due to the heat of the laser, the depth it can be safely etched to etc.