I remember learning the rule for when to use cualquier, cualquiera, and cualesquiera, but was always confused about the exact differences. When should each be used, and what role do number, gender, ...
Here is an English example where someone is referring to a man as a turtle: That turtle is slow. He is angry because he will not win. (calling that man a turtle) In Spanish, the referenced ...
I have seen several times the use of @ instead of 'a' or 'o' for refering masculine and femenine words at the same time. For example: Hola a tod@s. Is this an accepted use?