There are a few similar words used in plurals.xml file of CLDR used by this
class. Following naming convention is used in the code (a name of
corresponding tag from xml file is provided in brackets, if any):
- ruleset: a set of plural rules for a locale [pluralRules]
- rule: a rule for one of the forms: zero, one, two, few, many [pluralRule]
- subrule: one of the conditions of rule. One rule can have many conditions
joined with "and" or "or" logical operator.