This is a thought I first shared at CakeFest Orlando this year, but could not explain properly at the time.

He illustrates with an example of a protected "balance" variable in a BankAccount class. Sure, it's marked as private but less skilled programmers might not use it that way. He recommends a method without the getters/setters to help make the usage of the variable a bit simpler. He also suggests that using protected/private scoping helps to promote "crappy code" - using them to provide a sort of protection for code that you either don't want getting used or hiding it away so the API can't get at it.

Anyhow, one annoying thing about SimpleXML has to do with caching. When using web services, we often cache the contents we get back. We were having a problem where we would get an error about a SimpleXML node not existing.

They were using memcache to store the information but came across problems when their code tried to use a (sometimes) empty tag. He gives two solutions - one using a recursive function that identifies the empty items and the other that encodes then decodes the object to and from JSON, keeping the values intact.