code: protected WebElement findElement(String by, String using, OperaWebElement el) {
      checkNotNull(using, "Cannot find elements when the selector is null");
      assertConnected();
  
      using = OperaStrings.escapeJsString(using);
      boolean isAvailable;
      Integer id;
      String script;
  
      if (el == null) {
        // Search the document
        script =
            "return " + OperaAtom.FIND_ELEMENT + "({\"" + by + "\": \"" + using + "\"})";
      } else {
        // Search within an element
        script =
            "return " + OperaAtom.FIND_ELEMENT + "({\"" + by + "\": \"" + using
            + "\"}, locator)";
      }
  
      if (el == null) {
        id = debugger.getObject(script);
      } else {
        id = debugger.executeScriptOnObject(script, el.getObjectId());
      }
  
      isAvailable = (id != null);
  
      if (isAvailable) {
        String error =
            debugger.callFunctionOnObject("return (locator instanceof Error) ? locator.message : ''",
                                          id);
        if (!error.isEmpty()) {
          throw new InvalidSelectorException(error);
        }
  
        Boolean isStale =
            Boolean.valueOf(debugger.callFunctionOnObject("locator.parentNode == undefined", id));
  
        if (isStale) {
          throw new StaleElementReferenceException("This element is no longer part of DOM");
        }
  
        return new OperaWebElement(this, id);
      } else {
        throw new NoSuchElementException("Cannot find element(s) with " + by);
      }
    }
docs: Find a single element using the selenium atoms.
  
  @param by    how to find the element, strings defined in RemoteWebDriver
  @param using the value to use to find the element
  @param el    the element to search within
  @return an element