The Gentoo PPC Handbook refers to "OldWorld", "NewWorld", and "Pegasos" (presumably some difference in Mac hardware) with no explanation of what they are. In contrast, the x86 version clearly explains that it needs to know the kind of processor. A list of Mac models and what kind they are might be nice, or at least an explanation of what the difference is. Reproducible: Always Steps to Reproduce:
You should know your PowerPC, as you also know your x86 (is it a 486, a Pentium-II, an Intel or an AMD?). If you don't know it, you can ask many websites about the difference. An explenation would only enlarge the handbook.