ATTRIBUTE_JTK_PORT_ID: "data-jtk-port-id" = "data-jtk-port-id"

Used to indicate what the port id should be for connections from/to this element. It does not necessarily mean that the connection will be attached to an element that has this attribute - it is possible to have 'logical' ports on some vertex, whose edges appear in the UI attached to the vertex, rather than some element inside the vertex. If you want to specify that some element is the place to which connections for a given port should be attached, use ATTRIBUTE_JTK_PORT (data-jtk-port)