Hi Alan,

The "A" prefix is the temporal annotation. The technical term is the
SignSpelling Sequence, which is used primarily for sorting. The "A"
prefix is an ordered list of symbols.
http://www.signwriting.org/archive/docs6/sw0534-SignSpellingGuidelines-2008.pdf

You can drop the "A" prefix if you only care about visual construction.

If we consider a longer example, such as "world":
AS18701S1870aS2e734S20500M18x33S1870an11x15S18701n18xn10S205008xn4S2e7340xn32

The "A" prefix always ends at an L, M, or R; as these are the markers
for the start of a signbox in the left, middle, or right lanes
respectively. In this example, the "A" prefix contains 4 symbol keys.
"A S18701 S1870a S2e734 S20500".

The rest of the example contains the spatial annotation: symbols with
coordinates.
M18x33S1870an11x15S18701n18xn10S205008xn4S2e7340xn32

A few quick rules
--------------
The x-axis is negative on the left and positive on the right.
The y-axis is negative on the top and positive on the bottom.
The symbols are positioned by the top-left of the symbol glyph.
The coordinate (0,0) is the center of a sign.


The first part "M18x33" tells us that the signbox is in the middle lane
with a max coordinate of (18,33).

The rest is simply symbols with coordinates:
S1870a n11x15 S18701 n18xn10 S20500 8xn4 S2e734 0xn32

The same string with explicit coordinates:
S1870a at (-11,15)
S18701 at (-18,-10)
S20500 at (8,-4)
S2e734 at (0,-32)

The complete "Hello world." example is online with the various notations:
http://www.signbank.org/SignPuddle1.6/canvas.php?ui=1&sgn=5&sid=663

Regards,
-Steve