/*
 * call-seq:
 *  from_document(doc)
 *
 * Create a new RelaxNG schema from the Nokogiri::XML::Document +doc+
 */
static VALUE from_document(VALUE klass, VALUE document)
{
  xmlDocPtr doc;
  Data_Get_Struct(document, xmlDoc, doc);

  // In case someone passes us a node. ugh.
  doc = doc->doc;

  xmlRelaxNGParserCtxtPtr ctx = xmlRelaxNGNewDocParserCtxt(doc);

  VALUE errors = rb_ary_new();
  xmlSetStructuredErrorFunc((void *)errors, Nokogiri_error_array_pusher);

#ifdef HAVE_XMLRELAXNGSETPARSERSTRUCTUREDERRORS
  xmlRelaxNGSetParserStructuredErrors(
    ctx,
    Nokogiri_error_array_pusher,
    (void *)errors
  );
#endif

  xmlRelaxNGPtr schema = xmlRelaxNGParse(ctx);

  xmlSetStructuredErrorFunc(NULL, NULL);
  xmlRelaxNGFreeParserCtxt(ctx);

  if(NULL == schema) {
    xmlErrorPtr error = xmlGetLastError();
    if(error)
      Nokogiri_error_raise(NULL, error);
    else
      rb_raise(rb_eRuntimeError, "Could not parse document");

    return Qnil;
  }

  VALUE rb_schema = Data_Wrap_Struct(klass, 0, dealloc, schema);
  rb_iv_set(rb_schema, "@errors", errors);

  return rb_schema;
}