How do the E commands in G-code work, exactly? I've tried looking online but haven't quite found the answer to what I'm confused about, exactly. Consider the following 3 lines of G-code:

G1 X129.000 Y126.322 E7.90758

G1 X128.349 Y125.707 F7800.000

G1 X128.476 Y125.548 E7.92045 F1800.000


Does the absence of an E command in the second line mean that no material is to be extruded from line 1 to line 2? As I understand it, the E parameter controls how much material has been extruded up to that line.

The reason why I am asking is because I'm trying to understand on the code level how to identify when a printer will travel without extruding any material, in the case of moving in the Z direction, or if you are printing multiple disconnected parts in one print. Since none of the Z lines seem to have any E commands, I'm inclined to believe that the absence of an E command means that when moving to the given position from the previous line, no material will be extruded. I've tried quite a few different queries online to try to discover if this is the case, but haven't found a simple answer, so I was hoping someone on this board could enlighten me.
Yes, the absense of an EX.XXX (or an EX.XXX with the same value as the previous one) means nothing will be extruded during the move. The extruder is treated as an imaginary fourth axis and works exactly the same as any other axis: if in a G1/G0 no new coordinate for it is specified, it retains its original position.