Support destination tags and X address in xrpl CAIP10 (#156)

Author: bumblefudge

xrpl/caip10.md

@@ -16,44 +16,78 @@ requires: ["CAIP-2", "CAIP-10"]
 ## Rationale
 
 In CAIP-10, a string-based general account address scheme is defined. XRPL
-addresses are identified by an address in the XRP Ledger's [base58btc][]
-encoding. The address is derived from an account's master public key. An XRPL
-address is a string with the following characteristics.
+supports two address formats:
+
+### Classic Addresses (r-addresses)
+
+Classic XRPL addresses are identified by an address in the XRP Ledger's [base58btc][]
+encoding. The address is derived from an account's master public key. A classic XRPL
+address is a string with the following characteristics:
+
 * It is between 25 and 35 characters long, inclusive.
-* It starts with the character `r`
-* It uses alpanumerical characters [excluding][base58btc] number `0`, lowercase
+* It starts with the character `r`.
+* It uses alphanumerical characters [excluding][base58btc] number `0`, lowercase
   letter `"l"` and capital letters `["O", "I"]`.
+* It is case-sensitive.
+* It includes a 4-byte checksum making the probability of generating a valid address from random characters approximately 1 in 2<sup>32</sup>.
+* It may optionally include a [destination tag][Destination Tags] in the form of a 32-bit unsigned integer appended with a hyphen (`-`) separator.
+
+### X-Addresses
+
+X-addresses are a newer format that encode both the destination address and an
+optional destination tag into a single string. An X-address has the following characteristics:
+
+* It starts with the character `X`
+* It uses base58 encoding (same character set as r-addresses)
 * It is case-sensitive
-* It includes a 4-byte checksum making the probabilty of generating a valid address from random characters approximately 1 in 2<sup>32</sup>
+* It encodes both the classic address and destination tag in a single value
+* It includes a checksum for validation
 
 ### Syntax
 
 The `account_id` is a case-sensitive string in the form:
-
+~~~~
 ```
 account_id:        chain_id + ":" + account_address
 chain_id:          See [CAIP-2][]
-account_address:   r[1-9a-hj-zA-HJ-NP-Z]{24,34}
+account_address:   classic_address | x_address
+classic_address:   r[1-9a-hj-zA-HJ-NP-Z]{24,34} + optional_tag
+optional_tag:      ("-" + [0-9]{1-10})?
+x_address:         X[1-9a-hj-zA-HJ-NP-Z]{46,47}
 ```
 
 ### Semantics
 
 The `chain_id` is specified by the [CAIP-2][] which describes the blockchain id.
-The `account_address` is the address to an account on the XRPL.
+
+The `account_address` represents an account on the XRPL and can be expressed in two formats:
+
+1. **Classic Address (r-address)**: A base58-encoded address optionally followed by a destination tag. The destination tag is a numeric identifier (0 to 2^32-1) used to identify a specific recipient or purpose at the destination address. When included, the tag is separated from the address by a hyphen (`-`).
+
+2. **X-Address**: A compact format that encodes both the classic address and destination tag (if any) into a single base58-encoded string starting with `X`. X-addresses eliminate the need for separate tag handling and reduce user error.
 
 ## Test Cases
 
 This is a list of manually composed examples
 
 ```
-# Livenet address
+# Livenet classic address (without tag)
 xrpl:0:r4FTvnahbUfhe1WK2EK5Jz4cNvdFvT8Dzt
 
-# Testnet address
+# Testnet classic address (without tag)
 xrpl:1:rEBakx2WdNsmRb5tm5KmhsqKAqvLJrRoiU
 
-# Devnet address
+# Devnet classic address (without tag)
 xrpl:2:rUgna78QFFeixu8v9ZqwtViWnknXYtHG2X
+
+# Classic address with destination tag
+xrpl:0:rPEPPER7kfTD9w2To4CQk6UCfuHM9c6GDY-495
+
+# X-address (Livenet)
+xrpl:0:XV5sbjUmgPpvXv4ixFWZ5ptAYZ6PD2q1qM6owqNbug8W6KV
+
+# X-address (Testnet)
+xrpl:1:TVE26TYGhfLC7tQDno7G8dGtxSkYQnSy8W3wYu
 ```
 
 ## Backwards Compatibility
@@ -64,15 +98,18 @@ Not applicable
 
 - [XRPL Address Definition][] - The explanation of a XRPL Address, what it consists of and what limitations it has.
 - [XRPL Base58 Encoding][] - Explains how a public key is encoded to a XRPL address.
+- [X-Address Format][] - Specification for the X-address format that encodes both address and destination tag.
+- [Destination Tags][] - Explanation of destination tags and their use in XRPL.
 
 
 [CAIP-2]: ./caip2.md
 [CAIP-10]: https://github.com/ChainAgnostic/CAIPs/blob/master/CAIPs/caip-10.md
 [base58btc]: https://en.bitcoin.it/wiki/Base58Check_encoding#Base58_symbol_chart
 [XRPL Address Definition]: https://xrpl.org/accounts.html#addresses
 [XRPL Base58 Encoding]: https://xrpl.org/base58-encodings.html
+[X-Address Format]: https://xrpaddress.info/
+[Destination Tags]: https://xrpl.org/source-and-destination-tags.html
 
 ## Copyright
 
 Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
-