sfio source internal to Graphviz is ~8 years older than source in github (https://github.com/att/ast/tree/master/src/lib/libast/sfio)
Steps to reproduce
compared sfio.h within Graphviz to sfio.h from github
Expected identical (or similar) versions
github version: #define SFIO_VERSION 20090915L Graphviz Version #define SFIO_VERSION 20010201L
Diff of files shows differences. I have not tried to determine if any Graphviz-related bugs are fixed in the newer version of sfio.