In this answer, there are edges with :e and :w in the code:
key:i1:e -> key2:i1:w
What do they mean? I suppose they are this line in The DOT Language | Graphviz:
compass_pt : (n | ne | e | se | s | sw | w | nw | c | _)
But I don't understand this. Googling compass_pt GraphViz doesn't yield any useful information.
See https://www.graphviz.org/doc/info/attrs.html#k:portPos
Ports are used to explicitly position head/tail of edges. Ports are specified by compass points n(north), sw (southwest), etc and denote where on a node the edge is to terminate.
graph p {
// node names (e.g. ne) are not Graphviz instructions, but are just for the reader
n--P:n
ne--P:ne
nw--P:nw
s--P:s
se--P:se
sw--P:sw
w--P:w
e--P:e
c--P:c
}
gives:
