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In the LibreOfficeDev Calc functions, parameters marked as "optional" can be omitted only when no parameter follows. For example, in a function with four parameters, in which the last two parameters are marked as "optional", you can omit parameter 4 or parameters 3 and 4, but you cannot omit parameter 3 alone.
Codes greater than 127 may depend on your system's character mapping (for example iso-8859-1, iso-8859-2, Windows-1252, Windows-1250) and hence may not be portable.