This variable holds the current position (moment) a time line is
currently at. You can change this value to skip parts of the time
line, or to repeat parts or to start the time line again from the
timeline_position = 0;
timeline_running = true;
The above code will check to see if the instance is running a time line, and if it is not then it resets the assigned time line to start at the first moment and then starts it.