code: private BigInteger parseCharacter(String input) {
  		int pos = 1;
  		char c = input.charAt(pos++);
  		if (c == '\\') {
  			// escape code
  			switch (input.charAt(pos++)) {
  			case 'b':
  				c = '\b';
  				break;
  			case 't':
  				c = '\t';
  				break;
  			case 'n':
  				c = '\n';
  				break;
  			case 'f':
  				c = '\f';
  				break;
  			case 'r':
  				c = '\r';
  				break;
  			case '"':
  				c = '\"';
  				break;
  			case '\'':
  				c = '\'';
  				break;
  			case '\\':
  				c = '\\';
  				break;
  			default:
  				throw new RuntimeException("unrecognised escape character");
  			}
  		}
  		return BigInteger.valueOf(c);
  	}
docs: Parse a character from a string of the form 'c' or '\c'.
  
  @param input
  @return