1.2. Field Matcher

The field matcher allows you to define criteria that must apply to variable fields. There are four different types:

• exists matcher checks whether a field exists or not

• control field predicate operates on control fields

• data field predicate operates on data fields

• count predicate checks whether a specific number of fields are present

Control and data fields are identified by three-digit tags. Only numeric digits from 0 to 9 are permitted in each position. If a tag begins with two zeros, it is a control field; otherwise, it is a data field. A data field is additionally identified by two indicators. Valid values for an indicator are a to z, 0 to 9, and a space (U+0020).

A tag matcher is used to select the fields to which the field matcher will be applied. When using a data field matcher, you can also specify a indicator matcher to define the indicator assignments.