The documentation says the default value for "tooltip" is the empty string , and that "If unset, Graphviz will use the object's label if defined" .
If I want no tooltips, it seems natural to say
but that has no effect because that's the default. If I look at output from -Tcanon I see Graphviz even strips it out.
It would make more sense to me to define the default for "tooltip" as "\L" . Remove the "If unset..." sentence from the tooltip definition. And thus let me set "tooltip" to the empty string to indicate that I want no tooltips.
[erg] This is somewhat related to problem of node labels, and that the graph library treats an empty string as undefined.