text: public static void registerFunction(String name, Function func){FunctionMetadata metaData = FunctionMetadataRegistry.getFunctionByName(name);if(metaData == null) {if(AnalysisToolPak.isATPFunction(name)) {throw new IllegalArgumentException(name + " is a function from the Excel Analysis Toolpack. " +"Use AnalysisToolpack.registerFunction(String name, FreeRefFunction func) instead.");}throw new IllegalArgumentException("Unknown function: " + name);}int idx = metaData.getIndex();if(functions[idx] instanceof NotImplementedFunction) {functions[idx] = func;} else {throw new IllegalArgumentException("POI already implememts " + name +". You cannot override POI's implementations of Excel functions");}}