parse_memory(VALUE klass, VALUE data, VALUE encoding)
{
  htmlParserCtxtPtr ctxt;

  if (NIL_P(data)) {
    rb_raise(rb_eArgError, "data cannot be nil");
  }
  if (!(int)RSTRING_LEN(data)) {
    rb_raise(rb_eRuntimeError, "data cannot be empty");
  }

  ctxt = htmlCreateMemoryParserCtxt(StringValuePtr(data),
                                    (int)RSTRING_LEN(data));
  if (ctxt->sax) {
    xmlFree(ctxt->sax);
    ctxt->sax = NULL;
  }

  if (RTEST(encoding)) {
    xmlCharEncodingHandlerPtr enc = xmlFindCharEncodingHandler(StringValueCStr(encoding));
    if (enc != NULL) {
      xmlSwitchToEncoding(ctxt, enc);
      if (ctxt->errNo == XML_ERR_UNSUPPORTED_ENCODING) {
        rb_raise(rb_eRuntimeError, "Unsupported encoding %s",
                 StringValueCStr(encoding));
      }
    }
  }

  return Data_Wrap_Struct(klass, NULL, deallocate, ctxt);
}
The software does not handle or incorrectly handles when a particular element is not the expected type, e.g. it expects a digit (0-9) but is provided with a letter (A-Z).