Turns off processing of prefix characters. Typically, the ampersand (&) mnemonic-prefix character is interpreted as a directive to underscore the character that follows, and the double-ampersand (&&) mnemonic-prefix characters as a directive to print a single ampersand. By specifying TextFormatFlags.NoPrefix, this processing is turned off. For example, an input string of "A&bc&&d" with TextFormatFlags.NoPrefix applied would result in output of "A&bc&&d".