HRL is similar to XRL and TRL - in that it will evaluate an HDS structure, locate embedded requests, issue the request and substitute the response into the HDS structure.
Like XRL/TRL it is recursive and substitutions are recursively evaluated. In addition it supports the NetKernel declarative request syntax for specifying resource requests for inclusions.
Being recursive and consisting of requests into the NetKernel ROC space, each substitution is actually a cacheable resource. Therefore HRL is very high-performance in dynamic applications since only the parts of a recursion tree that are not already cached will require computation.