code: function TimelineSegment(key, start, duration, transition, compiler) {
    this.key = key;
    this.start = start;
    this.duration = duration;
    this.transition = transition;
    this.compiler = compiler;
  
    this.trail = 0;
  }
docs: A timeline transition segment. An instance of this class is created internally when calling {@link THREE.BAS.Timeline.add}, so you should not use this class directly.
  The instance is also passed the the compiler function if you register a transition through {@link THREE.BAS.Timeline.register}. There you can use the public properties of the segment to compile the glsl string.
  @param {string} key A string key generated by the timeline to which this segment belongs. Keys are unique.
  @param {number} start Start time of this segment in a timeline in seconds.
  @param {number} duration Duration of this segment in seconds.
  @param {object} transition Object describing the transition.
  @param {function} compiler A reference to the compiler function from a transition definition.
  @constructor