public String value() {
            return value;
        }
Constant value can be:

<ol>
  <li>List of values (a,b,c)
  <li>Range of values (m AND n)
  <li>A value (x)
  <li>A value is either a string or a number
</ol>
es6-persistence/src/main/java/com/netflix/conductor/es6/dao/query/parser/internal/ConstValue.java