The function terminated_by identifies how a record is terminated. Records can be terminated by a byte constant or EOF (end of file). The constant can be declared numerically (decimal or hexadecimal), or as a plain ASCII char. In the latter case, the literal must be enclosed in quotes.

external myExternal : terminated_by(0xA) {
     // <contents declaration>
};
external myExternal : terminated_by(';') {
     // <contents declaration>
};

external demoExt : terminated_by(EOF) {
    // <contents declaration>
    ascii remainingData : dynamic_size( remaining_size );
};

Binary encodings that vary in size often contain a field with information on their specific length. In these cases, the dynamic_size declaration may be used, specifying how to calculate the record size from the values of one or more fields.

external myExternal : dynamic_size(recordLength) {
    int RecordLength : static_size(2);
   // <continued contents declaration>
};

static_size

Records of fixed size are declared using static_size.

external myExternal : static_size(<recordLength>) {
     // <contents declaration>
};

If the identified_by option is present, it specifies the condition under which a record of this type is present in the stream. This is used when the input data contains different record types, in which case the decoder uses the identified_by expression to evaluate if the data matches the record type.

The condition is also evaluated when deciding whether to use a specific out map during encoding.

external myUDRType1 : identified_by( udrType == 1 ) {
  int udrType : static_size(1);
  // <continued contents declaration>
};