boolean isLiteral(int index){
  if (isValidMask() && index < string.length()) {
    return literalMask.get(index);
  }
  return false;
}

boolean isLiteral ( int index ) { if ( isValidMask ( ) && index < string . length ( ) ) { return literalMask . get ( index ) ; } return false ; }
returns true if the character at index is a literal , that is not editable .
