Font switching can be prevented and the escape character output by doubling it (for example, %%). Invalid codes (for example, %51) are output literally. The font switching character sequence does not have to be preceded or followed by blank characters. For example ‘ABC%04DEF%pGHI’ is output as the 9-character string ‘ABCDEFGHI’ with the two sub-strings ‘ABC’ and ‘GHI’ in the principal font, and the middle three characters (for example, ‘DEF’) in variation 4 (for example, upright bold) of the principal font.