Having a metanode like this:
{ [In,Parameter] -> Transformation -> Out}
One can easily omit explicit Input and Output declaration since constructed graph implicitly has this information:
{ [in,Parameter] -> Transformation -> out}
By this rule, every source node without explicit Input type is an Input. And vice versa, every sink node without explicit Output type is an Output.
What to do when node is source AND sink at the same time?