Is a mixture of exclamation mark and question mark accepted practice, or was it a typo?

Question

Sometimes in English we write statements such as:

What the heck is going on here?!

(ending with both an exclamation mark and a question mark).

I saw a sentence like this in a Spanish book:

¡Qué estás haciendo?

(that wasn't the exact sentence - I don't recall it - but it either started with an inverted exclamation point, and ended with a question mark, or vice versa (started with inverted question mark, and ended with an exclamation mark).

Was this a typo, or is that standard Spanish punctuation for rare cases (I say rare, because it's the first time I've ever seen it)?

If it is correct, I wonder why it doesn't follow this pattern instead:

¡¿Qué estás haciendo?!

?!?

Answer 1

To my surprise, it is correct:

interrogación y exclamación (signos de)

1. Los signos de interrogación (¿?) y de exclamación (¡!) sirven para representar en la escritura, respectivamente, la entonación interrogativa o exclamativa de un enunciado. Son signos dobles, pues existe un signo de apertura y otro de cierre, que deben colocarse de forma obligatoria al comienzo y al final del enunciado correspondiente.

(...)

3. Usos especiales

   (..)

   b) Cuando el sentido de una oración es interrogativo y exclamativo a la vez, pueden combinarse ambos signos, abriendo con el de exclamación y cerrando con el de interrogación, o viceversa: ¡Cómo te has atrevido? / ¿Cómo te has atrevido!; o, preferiblemente, abriendo y cerrando con los dos signos a la vez: ¿¡Qué estás diciendo!? / ¡¿Qué estás diciendo?!

As you see, RAE says that it is preferred to keep signs balanced (ie, closing as many as you open), but it is also accepted to open with one and closing with the other.