Clarifying the 'padding alist-key

[Mark Polesky]

Okay, the description I wrote for the 'padding key of the
spacing alists is clearly incorrect, especially the bit
about the "unobstructed (invisible) rectangle":

"padding – the minimum required amount of unobstructed
vertical whitespace between two items, measured in
staff-spaces.  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."

I think that one of the two descriptions below should do.
But which one is better?

1)
padding – the minimum required amount of vertical whitespace
between two items, measured in staff-spaces.  When
available, skylines are used in the spacing calculation.

2)
padding – the minimum required amount of vertical whitespace
between the skylines of two items, measured in staff-spaces.

Thanks.
- Mark