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 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.