-Specifies how to calculate the space between a title (or top-level markup)
-and the system that follows it. This is an associative list with five
-components:
-@itemize @bullet
-@item @var{space} -- the amount of stretchable space between the baseline
-of a title and the center of the staff that follows it;
-@item @var{padding} -- the minimum amount of whitespace that must be
-present between a title and the staff that follows it;
-@item @var{stretchability} -- the ease with which the stretchable
-space increases when a page is stretched.
-If this is zero, the distance to the next staff will not stretch at all;
-@item @var{minimum-distance} -- the minimum distance to place between
-the baseline of a title and the center of the staff that follows it. This differs
-from @var{padding} in that the height of a staff has no effect on
-the application of @var{minimum-distance} (whereas the height of a
-staff is crucial for @var{padding}).
+
+@subsubheading Flexible vertical dimensions
+
+In most cases, it is preferable for the vertical distances between
+certain items (such as margins, titles, systems, and separate
+scores) to be flexible, so that they stretch and compress nicely
+according to each situation. A number of @code{\paper} variables
+(listed below) are available to fine-tune the stretching behavior
+of these dimensions.
+
+Each of these variables is an associative list containing four
+@emph{keys}:
+
+@itemize
+@item @code{padding} -- the minimum required amount of
+unobstructed vertical whitespace between two items. This can be
+thought of as the minimum height of an unobstructed (invisible)
+rectangle that extends from the leftmost to the rightmost point of
+the combined items.
+
+@item @code{space} -- the default vertical distance between the
+@emph{reference points} of the two items, when no collisions would
+result, and no stretching or compressing is in effect. The
+reference point of a title or markup is its highest point, and the
+reference point of a system is the middle line of the nearest
+staff. Values for @code{space} that are less than either
+@code{padding} or @code{minimum-distance} are not meaningful,
+since the resulting space will never be less than either
+@code{padding} or @code{minimum-distance}.
+
+@item @code{minimum-distance} -- the minimum required vertical
+distance between the reference points of the two items, when
+compressing is in effect. Values for @code{minimum-distance} that
+are less than @code{padding} are not meaningful, since the
+resulting space will never be less than @code{padding.}
+
+@item @code{stretchability} -- the stretchable space's propensity
+to stretch. If zero, the space will not stretch (unless
+collisions would result). When positive, the significance of a
+particular dimension's @code{stretchability} value lies only in
+its relation to the @code{stretchability} values of the other
+dimensions. For example, if one dimension has twice the
+@code{stretchability} of another, it will stretch twice as easily.
+Values should be non-negative and finite. The value @code{+inf.0}
+triggers a @code{programming_error} and is ignored, but
+@code{1.0e7} can be used for an almost infinitely stretchable
+spring. If unset, the default value is set to @code{space}. Note
+that the stretchable space's propensity to @emph{compress} cannot
+be directly set by the user and is equal to
+(@code{space}@tie{}@minus{}@tie{}@code{minimum-distance}).
+
+@end itemize
+
+If a page has a ragged bottom, the resulting distance is the
+largest of:
+
+@itemize
+@item @code{space},
+@item @code{minimum-distance}, and
+@item @code{padding} plus the smallest distance necessary to
+eliminate collisions.