Two things to note:

a) depending on your locale, \d might also match exponents. One sure fire way is to explicitly declare 0-9 instead.

b) If you place the dash as the very first or very last character within the character class, you do not need to escape it, as regex will treat it as a literal, and not a range.

@f3nd3r

The difference between [] and () is simple. [] is a character class. This checks for a single character at the current location in a string. So if I have x[ab]z for example, what this means, is match an x, followed by either an a or b (but not both, as this is for a single character), followed by a z. When dealing with (), we are talking about group caturing. This matches whatever is found inside and stored as a variable (which can be reused in the expression as a backreference). A more detailed explanation can be found here:
http://www.regular-expressions.info/brackets.html