The REQUIRED COMBINATIONS: subsection is used to specify any combinations of two words that must always appear together in a human-readable label. This subsection states criteria for well formed labels. This section can contain zero or more required combination specifications. Each required combination is specified on a separate line following the REQUIRED COMBINATIONS: keyword. Each such line should consist of exactly two label words, and is taken to mean that the first word, if present, must be combined with the second word. Any required prefixes or suffixes must also be specified. Any number of lines containing required combinations can be specified. The end of the list is taken to be a line starting with the COMBINATION CONSTRAINTS: keyword.
Note that required combinations are not bidirectional. That is, the required combination:
means that WORD1 cannot appear without WORD2, but does not mean that WORD2 cannot appear without WORD1.
Required combinations are automatically enforced during translation from human-readable to internal formats. Thus, given the above example, if the label TS WORD1 were entered, the translation would automatically add WORD2 to the label.
General Considerations for Specifying Encodings discusses some very important considerations concerning the specification of required combinations.