I ran into a stubborn issue with the sites favicon.ico file being reported as an issue by the GTMetrix testing tool under “Specify a cache validator”.
Specify a cache validator:
The following resources are missing a cache validator. Resources that do not specify a cache validator cannot be refreshed efficiently. Specify a Last-Modified or ETag header to enable cache validation for the following resources:
It’s a minor issue, one tiny file apparently not being cached, but I’m supposed to be an SEO expert, so should be able to fix this :-).
Continue Reading How to Fix a Specify a Cache Validator Warning in WordPress