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Trend Database Guide and Reference
Preface : Examples of syntax descriptions : Complex syntax descriptions with both required and optional elements
 

Complex syntax descriptions with both required and optional elements

Some syntax descriptions are too complex to distinguish required and optional elements by bracketing only the optional elements. For such syntax, the descriptions include both braces (for required elements) and brackets (for optional elements).
In this example, ASSIGN requires either one or more field entries or one record. Options available with field or record are grouped with braces and brackets:

Syntax

ASSIGN   { [ FRAME frame ] { field [ = expression ] }
            [ WHEN expression ] } ...
      | { record [ EXCEPT field ... ] }