I am working on an Intranet with nested frames, and am unable to access a child frame.

The HTML source:

```html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
 <head>
  <meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
  <title>VIS</title>
  <link rel="shortcut icon" href="https://bbbbb/ma1/imagenes/iconos/favicon.ico">
 </head>
 <frameset rows="51,*" frameborder="no" scrolling="no" border="0">
  <frame id="cabecera" name="cabecera" src="./blablabla.html" scrolling="no" border="3">
   <frameset id="frame2" name="frame2" cols="180,*,0" frameborder="no" border="1">
    <frame id="menu" name="menu" src="./blablabla_files/Menu.html" marginwidth="5" scrolling="auto" frameborder="3">
     <a href="/ma1/jsp/orD/queda.jsp" target="contenido">Buscar</a>
    <frame id="contenido" name="contenido" src="./blablabla_files/saved_resource.html" marginwidth="5" marginheight="5">
     <html>
      <head>
       <meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
       <title>BUSCAr</title>
      </head>
      <frameset name="principal" rows="220,*" frameborder="NO">
        <frame name="Formulario" src="./BusquedaSimple.html" scrolling="AUTO" noresize="noresize">
        <input id="year" name="year" size="4" maxlength="4" value="" onchange="javascript:Orden();" onfocus="this.value='2018';this.select();" type="text">
        <frame name="Busqueda" src="./saved_resource(2).html" scrolling="AUTO">
      </frameset>
      <noframes>
       &lt;body&gt;
       &lt;p&gt;soporte a tramas.&lt;/p&gt;
       &lt;/body&gt;
      </noframes>
     </html>
    <frame name="frameblank" marginwidth="0" scrolling="no" src="./blablabla_files/saved_resource(1).html">
   </frameset>
   <noframes>
     &lt;P&gt;Para ver esta página.&lt;/P&gt;
   </noframes>
 </frameset>
</html>
```

I locate the button "Buscar" inside of frame "menu" with:

```html
driver.switch_to_default_content()
driver.switch_to_frame(driver.find_element_by_css_selector("html frameset frameset#frame2 frame#menu"))
btn_buscar = driver.find_element_by_css_selector("#div_menu > table:nth-child(10) > tbody > tr > td:nth-child(2) > span > a")
btn_buscar.click()
```

I've tried this code to locate the input id="year" inside frame="Formulario": 

```html
driver.switch_to_default_content()
try:       driver.switch_to_frame(driver.switch_to_frame(driver.find_element_by_css_selector("html frameset frameset#frame2 frame#contenido frameset#principal frame#Formulario")))
    print("Ok cabecera -> contenido")
except:
    print("cabecera not found")
```

or

```html
driver.switch_to_frame(driver.switch_to_xpath("//*[@id='year"]"))
```

but they don't work.

Can you help me?

Thanks!