Hi Alan,

Thanks for the comments.  I'll try to integrate your ideas.  This is 
only a brief introduction to the SignWriting script.  The main purpose 
of the document is to describe a coded character set.

3 Types of graphemes
* The writing graphemes are used in clusters when writing a sign.

* The detailed location graphemes are used individually or in sequence, 
but not in a written text.  These graphemes represent analysis outside 
the cluster.

* The punctuation graphemes are used when writing text.  Always alone 
and always in the middle lane.

Of the 3 types of grapheme, only the writing graphemes are used in a 

Regarding a cluster, that's defined in the next section...

1.1.2.  Cluster

    The writing graphemes of the SignWriting script are arranged in spatial
    clusters on a variably sized 2 dimensional canvas.  Every cluster
    has two centers: absolute and artistic.

    The absolute center of a cluster is defined as the center of a
    bounding box: the smallest possible rectangle that encloses a set of
    graphemes.  Graphemes for the head and trunk are special for
    centering.  If a cluster includes any head or trunk graphemes, the
    bounding box is only placed around those head and trunk graphemes.
    Otherwise, the bounding box is placed around all of the graphemes in
    the cluster.

    The artistic center of a cluster is the grapheme that the other
    graphemes relate or revolve around.

Or you can read the entire working draft.  It's not done yet...