#define isIDFIRST_lazy(p) isIDFIRST_lazy_if(p,1)
#define isALNUM_lazy(p) isALNUM_lazy_if(p,1)
-/* how wide can a single UTF-8 encoded character become */
-#define UTF8_MAXLEN 13
-/* how wide a character can become when upper/lowercased */
-#define UTF8_MAXLEN_UCLC_MULT 3
-#define UTF8_MAXLEN_UCLC (UTF8_MAXLEN*UTF8_MAXLEN_UCLC_MULT)
-/* how wide a character can become when casefolded */
-#define UTF8_MAXLEN_FOLD_MULT 3
-#define UTF8_MAXLEN_FOLD (UTF8_MAXLEN*UTF8_MAXLEN_FOLD_MULT)
+#define UTF8_MAXBYTES 13
+/* How wide can a single UTF-8 encoded character become in bytes.
+ * NOTE: Strictly speaking Perl's UTF-8 should not be called UTF-8
+ * since UTF-8 is an encoding of Unicode and given Unicode's current
+ * upper limit only four bytes is possible. Perl thinks of UTF-8
+ * as a way to encode non-negative integers in a binary format. */
+#define UTF8_MAXLEN UTF8_MAXBYTES
+
+#define UTF8_MAXLEN_UCLC 3 /* Obsolete, do not use. */
+#define UTF8_MAXLEN_UCLC_MULT 39 /* Obsolete, do not use. */
+#define UTF8_MAXLEN_FOLD 3 /* Obsolete, do not use. */
+#define UTF8_MAXLEN_FOLD_MULT 39 /* Obsolete, do not use. */
+
+/* The maximum number of UTF-8 bytes a single Unicode character can
+ * uppercase/lowercase/fold into; this number depends on the Unicode
+ * version. An example of maximal expansion is the U+03B0 which
+ * uppercases to U+03C5 U+0308 U+0301. The Unicode databases that
+ * tell these things are UnicodeDatabase.txt, CaseFolding.txt, and
+ * SpecialCasing.txt. */
+#define UTF8_MAXBYTES_CASE 6
#define IN_BYTES (PL_curcop->op_private & HINT_BYTES)
#define DO_UTF8(sv) (SvUTF8(sv) && !IN_BYTES)