I'm looking to sort Library of Congress call numbers in Excel. The format of
the cdall numbers is:

Letters Number Period Letter Number

and after that, perhaps more periods, letters and numbers!

The problem seems to be that if I have (sorted):
C3.A40
C25.C25
C124.D45

attempting to sort them as text would list
C124.D45
C25.C25
C3.A40

Which is incorrect. I've been looking at the cell formatting features, and
they seem to only allow me to change how the data is displayed, not how Excel
thinks about the type of data.