Clarification.

include/fsm/print.h

@@ -87,11 +87,17 @@ struct fsm_hooks {
 
 /*
  * Print an FSM to the given file stream. The output is written in the format
- * specified by the lang enum. Not all languages support all options.
+ * specified by the lang enum.
+ *
+ * Not all languages support all options, and fsm_print will ENOTSUP where
+ * these are not possible. This is different to when an option is possible
+ * but simply not yet implemented, where fsm_print() will print a message
+ * to stderr and exit.
  *
  * The code generation for the typical case of matching input require the FSM
- * to be a DFA. As opposed to e.g. FSM_PRINT_API, which generates code for other
- * purposes, and does not place particular expecations on the FSM.
+ * to be a DFA, and will EINVAL if the FSM is not a DFA. As opposed to e.g.
+ * FSM_PRINT_API, which generates code for other purposes, and does not place
+ * particular expecations on the FSM.
  *
  * The output options may be NULL, indicating to use defaults.
  *