Documentation unclear regarding the Id attribute of a node.

[Dominic-Mayers]

The documentation says

"If you assign an id attribute to a vertex, this library will automatically use it as the vertex ID in the DOT output"

A dot string can contain an ID attribute for a vertex in the form

digraph {
  "Label" [id="nodeId" ...] 
}

and passing this to the dot executable with the option -Tsvg will create a element for the node with the same id, which can be used with getElementById( "nodeId"). However, when I use the command $node->setAttribute('id', $nodeId ); to add an Id to a vertex, the dot output (the string), does not contain the ID attribute for the node.