function extractExamples(grammarsDef) {
  const matchResult = grammars.OhmWithExamples.match(grammarsDef);
  if (matchResult.failed()) {
    throw new Error(matchResult.message);
  }
  return semantics(matchResult).examples();
}
@param {string} grammarsDef - A string containing one or more grammar definitions.
@return {[Example]}