FrameMensa Quiz #1 -- ANSWER (spoiler)

A few days ago I proposed this quiz:

  Work out how to format a document that comprises two kinds of paragraphs,
  so that ordinary body text and headings align with grid lines spaced
  vertically, on 18-point spacing.
  
  Each body line is to take 18 points of vertical space.
  Consecutive paragraphs are to be separated by a single blank line.
  
  Each heading line is to take two lines' worth of space, with the heading
  text in the middle of that space -- that is, the headings are displaced
  half a line from the rest of the text, spaced with a quarter line above
  and a quarter line below.
  
  Hint:
  
  If you put a 18 point Space Before a normal paragraph, and 18 points of 
  Space After, Frame overlaps these spaces.
  
  If you put 18 points of Space Before or After a normal paragraph the you
  will get the desired space between normal paragraphs, but an intervening
  Heading paragraph then has to contend with a minimum of 18 points of
  space above or below. An additional complexity is that Frame disregards
  Space Below a paragraph that falls at the top of a column. The formatting
  has to continue to function in this case.
  
One solution is to use a column arrangement -- on a master page, say --
that has thirty vertically-stacked text frames each 18 points high, each
designed to accommodate a single line. Assign to normal paragraphs a
leading of 18 points; this will allow only one line per text frame. In the
Advanced properties of the heading format, place a Frame Before that refers
to an empty frame 9 points in height. This will displace the headings down
the required amount. You will have to include after every heading paragraph
an empty paragraph, to occupy the text frame immediately below in order to
achieve the required spacing below a heading. But this solution is clumsy
and inefficient.

A better solution uses a character attribute that has almost no
documentation and almost no user interface: the badly-named "vertical
kerning", more properly called "baseline shift". 

Select a character and, on a Mac, hold Option and hit Down Arrow in the
inverted-T cursor arrow cluster. The character will be assigned a 1 point
baseline offset, downwards. If you hit Shift-Option-Down Arrow, the
character will be offset 6 points. If you use the Up Arrow key instead,
then you will obtain an upward shift. Remove the baseline offset by
hitting Option-Keypad 5.

The quiz is solved by:

- defining a normal paragraph to have 18 points space before, zero space
   after, and 18 point leading,

- defining a heading paragraph to have no space before or after, 18 point
   leading, and "keep with next", and

- giving heading paragraphs a downward baseline offset of 9 points.

Baseline offsets cannot be entered into the character or paragraph
catalogs using Frame's user interface, and cannot be copied from one
paragraph or character to another or from one entry in a catalog to
another. However, the attribute is saved in MIF as the FDY attribute,
which specifies downward shift as a percentage of font size. You can cheat
a little and edit the MIF file: apply a downward offset to a character and
save the document as MIF. Move the line containing the FDY attribute from
its location as an override to a particular character into the default
font section of the heading's paragraph format. When you import the
modified heading format, paragraphs using that default character format
will shift downward the required amount. This makes the solution is quite
automatic.

C.