This is a simple question concerning undefined articles usage. I have a doubt if the an should be used when the next word to it starts with vowel, or it is related to the noun.
I though it was related the the following word, if I used an adjective as the sentence:
undefined article old man
an old man
a old man
But I saw in this site that the author writes:
An RE (which means Regular Expression) what made question it.
a usage works?