ESI

Edge Side IncludesESI is an XML-based markup language that provides a means to assemble resources in HTTP clients. Unlike other in-markup languages, ESI is designed to leverage client tools like caches to improve end-user perceived performance, reduce processing overhead on the origin server, and enhanced availability. ESI allows for dynamic content assembly at the edge of the network, whether it is in a Content Delivery Network, end-user's browser, or in a Reverse Proxy right next to the origin server(Definition adapted from the original specification document)

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