range: a value goes to the first class (by value) whose upper bound
it does not exceed, values above the last bound to the last class.
exact: a value goes to the class of that value; other values are
transparent.
The classes, in any order.
Optionalminrange: the lower bound of the first class (values below it still go to the first class). Default: shown from the first bound.
OptionalmethodHow the classes were made, for an editor to offer the same again (manual: bounds set by hand). Not used to show them.
Classes of values and their colors.