Declared ETags, together with Russian Doll caching, can be used to automatically mix your template and asset versions into the ETags set in your controllers. This avoids the need to blow all browser caches on each deploy and neatly contains the scope of "freshness fallout" when you tweak a view.
To include the template's version in the ETag:
# Incorporate the cache version for this action into our ETag.
# This allows template changes to bubble up into HTTP cache
# freshness and bust browser caches when we make changes.