A number an expression stands for, as a ComplexInterval that holds it: in
double arithmetic rounded outward, with no settings read -- neither the precision of the
decimal evaluation nor the downcasting -- so that a question needing a dozen digits is
answered in a dozen and gets the same answer however the caller's settings are set. The
pilot of #1019's item 10, evaluation to a requested accuracy, for the checks inside the
library; EvalNumerical stays as it is beside it.