- (ptr - (current_buffer)->text->beg <= GPT_BYTE - BEG_BYTE ? 0 : GAP_SIZE) \
+ BEG_BYTE)
-/* Return character at byte position POS. */
+/* Return character at byte position POS. See the caveat WARNING for
+ FETCH_MULTIBYTE_CHAR below. */
#define FETCH_CHAR(pos) \
(!NILP (BVAR (current_buffer, enable_multibyte_characters)) \
/* Return character code of multi-byte form at byte position POS. If POS
doesn't point the head of valid multi-byte form, only the byte at
- POS is returned. No range checking. */
+ POS is returned. No range checking.
+
+ WARNING: The character returned by this macro could be "unified"
+ inside STRING_CHAR, if the original character in the buffer belongs
+ to one of the Private Use Areas (PUAs) of codepoints that Emacs
+ uses to support non-unified CJK characters. If that happens,
+ CHAR_BYTES will return a value that is different from the length of
+ the original multibyte sequence stored in the buffer. Therefore,
+ do _not_ use FETCH_MULTIBYTE_CHAR if you need to advance through
+ the buffer to the next character after fetching this one. Instead,
+ use either FETCH_CHAR_ADVANCE or STRING_CHAR_AND_LENGTH. */
#define FETCH_MULTIBYTE_CHAR(pos) \
(_fetch_multibyte_char_p = (((pos) >= GPT_BYTE ? GAP_SIZE : 0) \