The PipeOps of the input Graphs are not joined with new edges across
Graphs, so if length(graphs) > 1 the resulting Graph will be disconnected.
list of (Graph | PipeOp)
List of elements with one of the types defined above, which are the
Graphs to be joined. The list can be named, in which case the
IDs of the elements are prefixed with the names, separated by a dot (.).