anchor.diff:      | longYearScientific
       | seasonQualified
       ;
  -partialUncertainOrApproximate
  +partialUA
   	: MonthDayKnownYearUA | MonthDayKnownYearUAParenUA
   	| MonthKnownYearDayUA | MonthKnownYearDayUAParenUA
   	| YearDayKnownMonthUA | YearDayKnownMonthUAParenUA
  
positive.code: /**
   * This is an Antlr4 grammar for the Extended Date Time Format (EDTF)
   *
   * It's my first experience with Antlr so I'm sure there are many many
   * ways that it could be improved...
   *
   * EDTF specification website: http://www.loc.gov/standards/datetime/
   *
   * Author: Kevin S. Clarke (ksclarke@gmail.com)
   * Created: 2013/02/06
   * Updated: 2013/02/24
   *
   * License: BSD 2-Clause http://github.com/ksclarke/freelib-edtf/LICENSE
   */
  
negative.code: // ***********************   Level 2: Parser Rules   ************************ //
  
  level2Expression
      : partialUA
      | partialUnspecified
      | choiceList
      | inclusiveList
  