Test compatibility with caching plugins

[jbrinley]

Does this work with the various caching plugins? E.g., W3 Total Cache, WP Super Cache, etc.

• Do access controls still work?
• Do callbacks receive the appropriate arguments?
• Do routed paths, in fact, get cached?
• Are non-GET methods properly routed?

[jbrinley]

After some initial testing, pages do get cached.