- * Use: Formats a @printf@-like message and writes the result using
- * the given output operations. This is the backend machinery
- * for @dstr_putf@, for example.
+ * Use: Generic utility for mostly implementing the @nputf@ output
+ * function, if you don't have a better option.
+ *
+ * On entry, @*buf_inout@ should be null or a buffer pointer,
+ * with @*sz_inout@ either zero or the buffer's size,
+ * respectively. On exit, @*buf_input@ and @*sz_inout@ will be
+ * updated, if necessary, to describe a sufficiently large
+ * buffer, and the formatted string will have been written to
+ * the buffer.
+ *
+ * When the buffer is no longer required, free it using
+ * @x_free@.