OOXML spells eighteen cfRule types; fifteen of them are a predicate plus a style and are
modeled as ICondition + IConditionalFormat.getStyle. These three are not
boolean tests at all — they read the whole range and render across it — so they get their own
shape. The remaining OOXML type names are an IO concern and live in io-xlsx.
The three rules that are a value→visual mapping rather than a predicate.