The keywords "var" and "def" are used for declaring variables everywhere; the keywords "attribute" and "static" are
going away.  Variables declared inside a class are what used to be called attributes; variables defined at script level
are what used to be called statics; variables inside code blocks are local variables.  "Def" can be used wherever "var"
can, and it is an error to subsequently assign a value to a variable defined with "def".  Defs may be bound (which means
they are not truly constant.)  Status: var and def are valid anywhere, no warning yet for using "attribute" instead of
var, warning for using "static".  Static attributes should be turned into top-level vars or defs.