# Complexity as it relates to verifiers of languages

So I've been thinking about verifiers and a possible relation between a language's class and it's verifier complexity. From the book, "NP is the class of languages that have polynomial time verifiers". Is there an analog statement that can be said about a P-class verification complexity? Because P is a subset of NP, I understand that the statement of NP still applies to P. Still, my intuition is that there is something more that can be said about a verifier for P that relates to oracles. Is there more that can be said?

It is an open question whether $P=NL$, where $NL$ is the class of languages verifiable in logarithmic space. It is known that $NL \subseteq P$ (why?), and strongly suspected that $NL \neq P$, but we don't know for sure.