+ * - Calling `diff_flush()` will produce the output, it will call
+ * `diff_free()` to free any resources, e.g. those allocated in
+ * `diff_opt_parse()`.
+ *
+ * - Set `.no_free = 1` before calling `diff_flush()` to defer the
+ * freeing of allocated memory in diff_options. This is useful when
+ * `diff_flush()` is being called in a loop, rather than as a
+ * one-off. When setting `.no_free = 1` you must ensure that
+ * `diff_free()` is called at the end, either by flipping the flag
+ * before the last `diff_flush()` call, or by flipping it before
+ * calling `diff_free()` yourself.