The merge process aims to extract the maximum amount of information possible from this set of fields. Ideally the outcome will be a date, time or both, however there may be insufficient information to achieve this.
The process repeatedly calls the field rule {@link CalendricalRule#merge merge}method to perform the merge on each individual field. Sometimes two or more fields will combine to form a more significant field. Sometimes they will combine to form a date or time. The process stops when there no more merges can occur.
The process is based around hierarchies that can be combined. For example, QuarterOfYear and MonthOfQuarter can be combined to form MonthOfYear. Then, MonthOfYear can be combined with DayOfMonth and Year to form a date. Any fields which take part in a merge will be removed from the result as their values can be derived from the merged field.
The exact definition of which fields combine with which is chronology dependent. For example, see {@link ISOChronology}.
The details of the process are controlled by the merge context. This includes strict/lenient behavior.
The merge must result in consistent values for each field, date and time. If two different values are produced an exception is thrown. For example, both Year/MonthOfYear/DayOfMonth and Year/DayOfYear will merge to form a date. If both sets of fields do not produce the same date then an exception will be thrown. @throws CalendricalException if the merge cannot be completed successfully
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