Marc asked about drawing graphs with special handling using the WHERE clause in graphviz plugin's DSL.
Couldn't find the previous example, so recreating it here.
Sink: Elsewhere, Downstream
DOT digraph rankdir=LR node [shape=box style="rounded, filled"] edge [color=black] HERE NODE WHERE /^Source:/ node [fillcolor=palegreen] edge [color=palegreen] LINKS NODE -> HERE WHERE /^Sink:/ node [fillcolor=lightblue] edge [color=lightblue] LINKS HERE -> NODE
Source: can have many paragraphs starting with Source
Sink: and many Sink
DOT digraph rankdir=LR node [shape=box style="rounded, filled"] edge [color=black] HERE NODE WHERE /^Source:/ node [fillcolor=palegreen] edge [color=palegreen] LINKS NODE -> HERE WHERE /^Sink:/ node [fillcolor=lightblue] edge [color=lightblue] LINKS HERE -> NODE
For more information about using WHERE in algorithmic diagrams, see More About Algorithmic Markup