The only documentation currently available in these blog entries:
tests.js Various tests to ensure things are working
examples/example1.js Simple expression example from wikipedia article on PEGs.
examples/example2.js Expression example with actions used to produce AST.
examples/example3.js Expression example with actions used to evaluate as it parses.
examples/es3.js Incomplete/work-in-progress ECMAScript 3 parser (currently broken)
examples/es3_tests.js Tests for ECMAScript 3 parser
It has been updated to work in nodejs as well as in the browser.