This topic explains the deviations from the ISO 14977 specification in the EBNF format used by the Syntax Parsing Engine.
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Although the Syntax Parsing Engine conforms to the majority of the EBNF specification, there are some deviations introduced, which are listed in the table below:
The Syntax Parsing Engine allows the usage of the “?” character in special sequences, because the grammar properties section most likely contains regular expressions, which often use the “?” character. If the “?” were not allowed, all places where it is needed would need to be written as “?”, which is the XML escape sequence for the “?” character. This would cause all regular expression patterns to be less readable.
The Syntax Parsing Engine allows the usage of the underscore (“_”) in symbol names. Although the EBNF specification only allows symbol names to start with a letter, followed by zero or more letters or digits, the Syntax Parsing Engine extends this by allowing underscores anywhere in the symbol name. This is allowed to facilitate syntax tree pruning. See Pruning the Syntax Tree topic for more information.
The following topics provide additional information related to this topic.