note that Big-5 and HTML-like labels do not play together

Graphviz uses Expat for parsing HTML-like labels. Expat supports only the
encodings “US-ASCII”, “UTF-8”, “UTF-16”, and “ISO-8859-1”.¹ Using anything else
results in an error printed to stderr and Graphviz exiting.

¹ http://www.fifi.org/doc/libexpat1-dev/expat.html/index.html