I just re-read through portions of Friedl's book and I noticed something I missed previously.

.NET (Along with other platforms such as Java) allow for class subtraction.

Normally without class subtraction if you wanted to match any number except 4 you would need to do one of the following:

[0-35-9]

(?!4)\d

(?=[^4])\d

But with class subtraction (.NET example shown) you can also do this:

[\d-[4]]