"principle" vs "principal" failure

Chapter 2: Core foundations: building on C# 1: P51, section 2.4.1

Created: 1/15/2012
Last updated: 1/15/2012
Severity: Typo

The final sentence of page 51 reads:

Indeed, generics form one of the principle enhancements to the type system, which we'll look at next.

Oops - this should be principal instead:

Indeed, generics form one of the principal enhancements to the type system, which we'll look at next.