diff --git a/man/knit_cache_hook.Rd b/man/knit_cache_hook.Rd
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+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/cache.R
+\name{knit_cache_hook}
+\alias{knit_cache_hook}
+\title{Hook cache behavior}
+\usage{
+knit_cache_hook(x, nm, path, ...)
+}
+\arguments{
+\item{x}{a value of object to be cached.}
+
+\item{nm}{a name of the object to be cached. If a hook creates an external file based on \code{nm}, then apply \code{\link{URLencode}} to \code{nm} in order to avoid invalid file names.}
+
+\item{path}{a common path of the cache files of a chunk. If the hook creates extra
+files which needs be cleaned up by knitr, then create a directory whose
+name is `\code{path}` suffixed by "__extra", and save the files in it.}
+
+\item{...}{Reserved for future extensions}
+}
+\value{
+A value to be cached. If the value is the \code{knitr_cache_loader}-classed
+function, then the function is called and the returned value is treated as
+the loaded value. The loader should receive ellipsis as an argument for the
+future extentions.
+}
+\description{
+By default, a named list of objects in a chunk is cached as is in a rds
+file. If certain classes of objects need custom cache behaviors, register
+S3 methods to \code{knit_cache_preprocess}. The return value of the method
+is cached to the rds file. If custom loader is needed, the method should
+return a function with \code{knit_cache_loader} class which will be called.
+}
+\examples{
+registerS3method(
+  "knit_cache_preprocess",
+  "character",
+  function(x, nm, path, ...) {
+    # Cache x as is if it extends character class
+    if (!identical(class(x), "character")) {
+      return(x)
+    }
+
+    # Preprocess data (e.g., save data to an external file)
+    # Create external files under the directory of `paste0(path, "__extra")`
+    # if knitr should cleanup them on refreshing/cleaning cache.
+    d <- paste0(path, "__extra")
+    dir.create(d, showWarnings = FALSE, recursive = TRUE)
+    f <- file.path(d, paste0(URLencode(nm, reserved = TRUE), '.txt'))
+    writeLines(x, f)
+
+    # Return loader function
+    # which receives ellipsis for future extentions and has knit_cache_loader class
+    structure(function(...) readLines(f), class = 'knit_cache_loader')
+  },
+  envir = asNamespace("knitr")
+)
+}