A very common character class pattern you will come across in the world of regular expressions is [a-zA-Z] which is just matching the letters of the English alphabet in upper and lower case. Here’s a tip if you are going to use a range in a character class, especially of alpha characters, unless it matters to some other part of your pattern you may want to make the regex case sensitive. In the above example it only stops your pattern from being redundant which is reason enough since a case insensitive [a-z] or [A-Z] would match exactly the same characters. Another reason, and maybe a better one, is that it will save you some headaches if you deal with Unicode characters outside the ASCII range.
It only requires three keystrokes per cases and it allows you to limit the range to exactly what you specify in the pattern. That way you won’t have to sift through 65,000+ characters to find the one throwing things out of whack