* @return A collection of type descriptors generating implementation-dependent placeholders.
*/
protected Collection<ArgumentTypeDescriptor> getArgumentTypeDescriptors() {
return Arrays.asList( new VCFWriterArgumentTypeDescriptor(engine,System.out,argumentSources),
new SAMFileWriterArgumentTypeDescriptor(engine,System.out),
new OutputStreamArgumentTypeDescriptor(engine,System.out) );
}