astral plane

Incidentally, such beings may be said to have an existence of a sort upon the lower astral plane; they are elementals created by man's evil desires and unclean thoughts.

If your application works with MathML, or in various languages whose character sets gained support in Unicode 3.1 through the so-called Astral Planes, you will need to know that what Java calls a char is not really the same thing as a Unicode character or an XML character.