docs: private static char encodeChar(char c, int offset, boolean isDecodeNumber) {
  		if (isDecodeNumber) {
  			if (c >= CHAR0 && c <= CHAR9) {
  				c -= CHAR0;
  				c = (char) ((c + offset) % 10);
  				c += CHAR0;
  			}
  		}
  
  		// A == 65, Z == 90
  		if (c >= ACHAR && c <= ZCHAR) {
  			c -= ACHAR;
  			c = (char) ((c + offset) % 26);
  			c += ACHAR;
  		}
  		// a == 97, z == 122.
  		else if (c >= aCHAR && c <= zCHAR) {
  			c -= aCHAR;
  			c = (char) ((c + offset) % 26);
  			c += aCHAR;
  		}
  		return c;
  	}