+/*
+ Springs help chains of objects, such as the notes in a line of music,
+ distribute themselves evenly.
+ Each spring decides the length from the reference point of one object
+ along the line to the reference point of the next, based on a force
+ applied to the entire chain (see Spring::length() for details):
+ length = distance_ + flexibility * force
+
+ distance_ is the ideal separation between reference points
+ inverse_stretch_strength_ is the flexibility when the force is stretching
+ inverse_compress_strength_ is the flexibility when the force is compressing
+ min_distance_ sets a lower limit on length
+
+ Typically, the force applied to a list of objects ranges from about
+ -1 to about 1, though there are no set limits.
+*/
+