+/**
+ * The diff API is for programs that compare two sets of files (e.g. two trees,
+ * one tree and the index) and present the found difference in various ways.
+ * The calling program is responsible for feeding the API pairs of files, one
+ * from the "old" set and the corresponding one from "new" set, that are
+ * different.
+ * The library called through this API is called diffcore, and is responsible
+ * for two things.
+ *
+ * - finding total rewrites (`-B`), renames (`-M`) and copies (`-C`), and
+ * changes that touch a string (`-S`), as specified by the caller.
+ *
+ * - outputting the differences in various formats, as specified by the caller.
+ *
+ * Calling sequence
+ * ----------------
+ *
+ * - Prepare `struct diff_options` to record the set of diff options, and then
+ * call `repo_diff_setup()` to initialize this structure. This sets up the
+ * vanilla default.
+ *
+ * - Fill in the options structure to specify desired output format, rename
+ * detection, etc. `diff_opt_parse()` can be used to parse options given
+ * from the command line in a way consistent with existing git-diff family
+ * of programs.
+ *
+ * - Call `diff_setup_done()`; this inspects the options set up so far for
+ * internal consistency and make necessary tweaking to it (e.g. if textual
+ * patch output was asked, recursive behaviour is turned on); the callback
+ * set_default in diff_options can be used to tweak this more.
+ *
+ * - As you find different pairs of files, call `diff_change()` to feed
+ * modified files, `diff_addremove()` to feed created or deleted files, or
+ * `diff_unmerge()` to feed a file whose state is 'unmerged' to the API.
+ * These are thin wrappers to a lower-level `diff_queue()` function that is
+ * flexible enough to record any of these kinds of changes.
+ *
+ * - Once you finish feeding the pairs of files, call `diffcore_std()`.
+ * This will tell the diffcore library to go ahead and do its work.
+ *
+ * - Calling `diff_flush()` will produce the output.
+ */
+