The question mark is often utilized as a wildcard character: a symbol that can be used to substitute for any other character or characters in a string. In particular "?" is used as a substitute for any one character as opposed to the asterisk, "*", which can be used as a substitute for zero or more characters in a string. The inverted question mark (¿) corresponds to Unicode code-point U+00BF ¿ INVERTED QUESTION MARK (HTML ¿ · ¿), and can be accessed from the keyboard in Microsoft Windows on the default US layout by holding down the Alt and typing either 1 6 8 (ANSI) or 0 1 9 1 (Unicode) on the numeric keypad. In GNOME applications on GNU Linux operating systems, it can be entered by typing the hexadecimal Unicode character (minus leading zeros) while holding down both Ctrl and Shift, I J mm. e. : Ctrl Shift B F. In recent XFree86 and X. Org incarnations of the X Window System, it can be accessed as a compose sequence of two straight question marks, i. e. pressing Compose ? ? yields ¿. In classic Mac OS and Mac OS X (macOS), the key combination Option Shift ? produces an inverted question mark.