self-interpreter

Is it legal to call a C compiler written in C or a PHP interpreter written in PHP metacircular? Is this definition valid only for languages of a specific type, like Lisp? In short, what are the conditions that an interpreter should satisfy for being called Metacircular? A metacircular interpreter is an interpreter written in a (possibly more basic) implementation of the same language. This is usually done to experiment with adding new features to a language, or creating a different dialect. The reason this process is associated with Lisp is because of the highly lucid paper "The Art of the