9. The computer readable storage medium according to claim 1 , wherein the program causes the computer to perform further operations comprising: receiving an instruction to delete the fixed character string; identifying a character string preceding the fixed character string to be deleted and a character string following the fixed character string to be deleted; determining whether or not the character string preceding the fixed character string to be deleted and the character string following the fixed character string to be deleted are connectable to each other; and when it is determined that the character strings preceding and following the fixed character string to be deleted are connectable to each other, changing the fixed character string to be deleted into an unfixed character.
9. The computer readable storage medium according to claim 1 , wherein the program causes the computer to perform further operations comprising: receiving an instruction to delete the fixed character string; identifying a character string preceding the fixed character string to be deleted and a character string following the fixed character string to be deleted; determining whether or not the character string preceding the fixed character string to be deleted and the character string following the fixed character string to be deleted are connectable to each other; and when it is determined that the character strings preceding and following the fixed character string to be deleted are connectable to each other, changing the fixed character string to be deleted into an unfixed character. 11. The computer readable storage medium according to claim 9 , wherein the program causes the computer to perform further operations comprising: when the character string preceding the fixed character string and the character string following the fixed character string are determined to be not connectable to each other, determining, as a connectable character string, a character string located at a rearmost position among character strings that precede the fixed character string and that are connectable to the character string following the fixed character string, and changing all character strings present between the connectable character string and the character string following the fixed character string, into unfixed characters.