connectionsin ？

in the sendto port trigger, there is a statament:
get(connectionsin(outobject( current , index)))==0
I wonder what is connectionsin. Thanks

connectionsin is an attribute. An attribute is a direct pointer to a standard node in the objecttree. So in this case it returns a direct pointer to the node connectionsin of the "outobject( current , index)"
This node can be found in the tree under the connections node and this connections node contains the information over the input, output and central port connections.

Steven

I have found some node can be referenced this way, i.e., offsetx(current).

But are there any document telling which node can be referenced this way?

main menu option Help > Attribute Hints

Hi, Phil, you mean every attribute can be referenced this way?

Every attribute in that list.