tailtarget
Browser window to use for the 
tailURL link
type: escString, default: <none>
If the edge has a tailURL, tailtarget determines which
window of the browser is used for the URL.
Setting tailtarget=_graphviz will open a new window if it doesn't already
exist, or reuse it if it does.
If undefined, the value of the target is used.
- Edges
Note: map, svg only.