-#define Cupper(x) Ccat(x, _C_UPPER)
-#define Clower(x) Ccat(x, _C_LOWER)
-#define Calpha(x) Ccat(x, _C_ALPHA)
-#define Calnum(x) Ccat(x, _C_ALNUM)
-#define Cprint(x) Ccat(x, _C_PRINT)
-#define Cdigit(x) Ccat(x, _C_DIGIT)
-#define Cxdigit(x) Ccat(x, _C_XDIGIT)
-#define Cword(x) Ccat(x, _C_WORD)
-#define Cblank(x) Ccat(x, _C_BLANK)
-#define Cctrl(x) Ccat(x, _C_CTRL)
+#define Cupper(x) Ccat(x, _C_UPPER) /** Checks for an upper-case character (`A-Z`). **/
+#define Clower(x) Ccat(x, _C_LOWER) /** Checks for a lower-case character (`a-z`). **/
+#define Calpha(x) Ccat(x, _C_ALPHA) /** Checks for an alphabetic character (`a-z`, `A-Z`). **/
+#define Calnum(x) Ccat(x, _C_ALNUM) /** Checks for an alpha-numeric character (`a-z`, `A-Z`, `0-9`). */
+#define Cprint(x) Ccat(x, _C_PRINT) /** Checks for printable characters, including 8-bit values (`\t`, `0x20-0x7E`, `0x80-0xFF`). **/
+#define Cdigit(x) Ccat(x, _C_DIGIT) /** Checks for a digit (`0-9`). **/
+#define Cxdigit(x) Ccat(x, _C_XDIGIT) /** Checks for a hexadecimal digit (`0-9`, `a-f`, `A-F`). **/
+#define Cword(x) Ccat(x, _C_WORD) /** Checks for an alpha-numeric character or an inner punctation (`a-z`, `A-Z`, `0-9`, `_`). **/
+#define Cblank(x) Ccat(x, _C_BLANK) /** Checks for a white space (`0x20`, `\t`, `\n`, `\r`, `0x8`, `0xC`). **/
+#define Cctrl(x) Ccat(x, _C_CTRL) /** Checks for control characters (`0x0-0x1F`, `0x7F`). **/