+/*
+ * Validate a single UTF-8 character.
+ * @s: Beginning of UTF-8 character.
+ * @e: End of string.
+ *
+ * If it's valid, return its length (1 thru 4).
+ * If it's invalid or clipped, return 0.
+ */
+int utf8_validate_char(const char *s, const char *e);
+