David Otton has shared a discovery he's come across in his development - user-defined classes are not derived from stdClass.

Many OO languages have the concept of a single base class from which all other classes are explicitly or implicitly descended. For example, Ruby, Java and .NET all have Object. It's a very common belief that PHP implements stdClass as a base class for all objects, but this is in fact not the case.

He illustrates with a code example showing the results of calls to instanceof with a normal user class and one that extends the stdClass object.