docs: invalid signature description (#21)

* docs: invalid signature description

Co-authored-by: Yukang <[email protected]>
---------

Co-authored-by: Yukang <[email protected]>

Author: XuJiandong

docs/advanced.md

@@ -21,10 +21,13 @@ A multisig configuration uses the following structure:
 Each field here serves a different purpose:
 
 * `S`: `S` represents a reserved field. It must be of value `0x80`, the value is intentially chosen to be different from the secp256k1 multisig lock deployed in CKB's genesis block.
-* `R`: `R` represents how many starting public keys are required. For example, in a 3-of-5 setup, one might want to say that signatures for public key A and B must always be present so as to unlock the cell. In this case one can put ublic key A and B at the start of the public key list, and then set `R` to 2.
+* `R`: `R` represents how many starting public keys are required. For example, in a 3-of-5 setup, one might want to say that signatures for public key A and B must always be present so as to unlock the cell. In this case one can put public key A and B at the start of the public key list, and then set `R` to 2.
 * `M`: `M` represents the threshold, meaning how many signatures must be provided to unlock the cell. For instance, in a 3-of-5 setup, `M` must be 3.
 * `N`: `N` represents the avialble public keys, in a 3-of-5 setup, `N` must be 5.
 
+If any signature fails verification, the entire process fails, even when the remaining signatures (more than `M`) are valid. 
+In the UTXO model, transactions can be validated off-chain by SDKs or tools, allowing invalid signatures to be removed before broadcasting to the P2P network. Therefore, the design enforces a strict limit: provide exactly $M$ signatures (no more, no less).
+
 `N` also denotes how many pairs of `param flag` and `public key` will follow. Each `param id` will be 1 byte, the higher 7 bit represents `param ID`, denoting the parameter set to use, the lowest bit is a signature flag, for multisig configuration, this bit is always 0. A public key can range from 48 to 64 depending on the parameter set. The exact of value in `param id` indicates the length of public key followed.
 
 ## Multisig ID, Param ID