In the animation player, I noticed the 'TIP' animation has two markers, START and STOP. The 'aim_rifle_space_ads' animation also has several markers, which I assume are used to blend the arm movements while aiming, but I don't quite understand how these markers are utilized in the code."
Ah i see. Those are custom timeline. It mainly use to play animation from certain timeline. Unfortunately we cannot call from this marker. To use it, open animation node in animationtree and set custom timeline from marker. Set desired start and stop of animation timeline and now that clip will only play that range of animation instead of full animations. Useful stuff.