I am the author of the site. In the meantime I have updated the site:
http://www.angelfire.com/sc3/elmag
and the page:
http://www.angelfire.com/sc3/elmag/files/EM05FL.pdf
You are wrong with this example. The field on the unit square is not static, for
a = (3,0,0), for v*t <= z < 1
a =...