Summary of the post by Ethereum

An item is defined to be:

• a byte array, or
• a list of items.

How to encode a byte array

1. An array containing a single byte in the range of [0x00, 0x7f] is its own encoding.
   1. 0x11 is 0x11.
   2. Note that 0x11 is technically a shorthand for {0x11}.
2. If a byte array has $\leq 55$ elements, the first byte is 0x80 + length and the byte array will follow.
   1. 0x111111 is 0x83111111.
   2. 0x111111 is technically a shorthand for the array {0x11, 0x11, 0x11}.
   3. 0x83 because 0x80 + 3 where 3 is the length of the byte array.
3. If the byte array has $\geq 56$ elements, the first byte is 0xb7 + length in bytes of the length, the second byte is the length and the rest is the byte array.
   1. 0x11111...11 where we have 100 11’s.
   2. In other words, the byte array {0x11, 0x11, ..., 0x11} (100 bytes).
   3. This is encoded as 0xb864 followed by 100 11’s.
   4. The length 100 is 64 in hex decimals.
   5. 64 is 1-byte long.
   6. 0xb8 = 0xb7 + 1.

How to encode a list of items

First, you must encode every item in the list.

1. If the combined length of all the encoded items is $\leq 55$, then the first byte is 0xc0 + combined length and the encoded items will follow.
   1. [0x11, 0x111111].
   2. The elements are encoded as 0x11 and 0x83111111.
   3. This is 5 bytes.
   4. So, the encoding is 0xc51183111111.
2. If the combined length of all the encoded items is $\geq 56$, then the first byte is 0xf7 + length in bytes of the combined lengths, the second byte is the combined length and the encoded items will follow.
   1. [0x11, 0x111111, 0x11...11] where the last byte array is the 100-byte array.
   2. The total length is 1 + 4 + 102 = 107.
   3. 107 is 6b in hex decimals, which is 1 byte.
   4. Therefore, we obtain 0xf86b1183111111b86411...11.