I created a notebook where I decided to learn functions in the guide NumberDigits. I decided to do this for a few reasons. One I am interested in coming up with good names for functions and names like IntegerReverse which do one thing very well that is very specific are a good way to discuss how to name functions. The other reason is that I can understand these functions and there have been several times including when I was writing this notebook with CountDigits and another post on Wolfram Community on visualizing Euler's number I saw someone else make where someone pointed out that you could use RealDigits and I post I made where someone pointed out that I could solve my problem with RealDigits so I decided to work through the guide to not miss any simple digit functions. The function IntegerReverse is discussed in Chapter 46 of an Elementary Introduction to the Wolfram Language by Stephen Wolfram: Writing Good Code. Stephen Wolfram also writes about the addition of NumberDigit in the blog post for 12.3 as a specific use case of RealDigits. There is one function that I don't have as strong an intuitive grasp on: MantissaExponent.