Mention the signed extensions in the reference docs (#4887)

Co-authored-by: gupnik <mail.guptanikhil@gmail.com>

docs/sdk/Cargo.toml

@@ -74,6 +74,9 @@ pallet-balances = { workspace = true, default-features = true }
 pallet-assets = { workspace = true, default-features = true }
 pallet-preimage = { workspace = true, default-features = true }
 pallet-transaction-payment = { workspace = true, default-features = true }
+pallet-asset-tx-payment = { workspace = true, default-features = true }
+pallet-skip-feeless-payment = { workspace = true, default-features = true }
+pallet-asset-conversion-tx-payment = { workspace = true, default-features = true }
 pallet-utility = { workspace = true, default-features = true }
 pallet-multisig = { workspace = true, default-features = true }
 pallet-proxy = { workspace = true, default-features = true }

docs/sdk/src/reference_docs/signed_extensions.rs

@@ -1,7 +1,59 @@
 //! Signed extensions are, briefly, a means for different chains to extend the "basic" extrinsic
 //! format with custom data that can be checked by the runtime.
 //!
-//! # Example
+//! # FRAME provided signed extensions
+//!
+//! FRAME by default already provides the following signed extensions:
+//!
+//! - [`CheckGenesis`](frame_system::CheckGenesis): Ensures that a transaction was sent for the same
+//!   network. Determined based on genesis.
+//!
+//! - [`CheckMortality`](frame_system::CheckMortality): Extends a transaction with a configurable
+//!   mortality.
+//!
+//! - [`CheckNonZeroSender`](frame_system::CheckNonZeroSender): Ensures that the sender of a
+//!   transaction is not the *all zero account* (all bytes of the accountid are zero).
+//!
+//! - [`CheckNonce`](frame_system::CheckNonce): Extends a transaction with a nonce to prevent replay
+//!   of transactions and to provide ordering of transactions.
+//!
+//! - [`CheckSpecVersion`](frame_system::CheckSpecVersion): Ensures that a transaction was built for
+//!   the currently active runtime.
+//!
+//! - [`CheckTxVersion`](frame_system::CheckTxVersion): Ensures that the transaction signer used the
+//!   correct encoding of the call.
+//!
+//! - [`CheckWeight`](frame_system::CheckWeight): Ensures that the transaction fits into the block
+//!   before dispatching it.
+//!
+//! - [`ChargeTransactionPayment`](pallet_transaction_payment::ChargeTransactionPayment): Charges
+//!   transaction fees from the signer based on the weight of the call using the native token.
+//!
+//! - [`ChargeAssetTxPayment`](pallet_asset_tx_payment::ChargeAssetTxPayment): Charges transaction
+//!   fees from the signer based on the weight of the call using any supported asset (including the
+//!   native token).
+//!
+//! - [`ChargeAssetTxPayment`(using
+//!   conversion)](pallet_asset_conversion_tx_payment::ChargeAssetTxPayment): Charges transaction
+//!   fees from the signer based on the weight of the call using any supported asset (including the
+//!   native token). The asset is converted to the native token using a pool.
+//!
+//! - [`SkipCheckIfFeeless`](pallet_skip_feeless_payment::SkipCheckIfFeeless): Allows transactions
+//!   to be processed without paying any fee. This requires that the `call` that should be
+//!   dispatched is augmented with the [`feeless_if`](frame_support::pallet_macros::feeless_if)
+//!   attribute.
+//!
+//! - [`CheckMetadataHash`](frame_metadata_hash_extension::CheckMetadataHash): Extends transactions
+//!   to include the so-called metadata hash. This is required by chains to support the generic
+//!   Ledger application and other similar offline wallets.
+//!
+//! - [`StorageWeightReclaim`](cumulus_primitives_storage_weight_reclaim::StorageWeightReclaim): A
+//!   signed extension for parachains that reclaims unused storage weight after executing a
+//!   transaction.
+//!
+//! For more information about these extensions, follow the link to the type documentation.
+//!
+//! # Building a custom signed extension
 //!
 //! Defining a couple of very simple signed extensions looks like the following:
 #![doc = docify::embed!("./src/reference_docs/signed_extensions.rs", signed_extensions_example)]

substrate/frame/system/src/extensions/check_mortality.rs

@@ -28,6 +28,9 @@ use sp_runtime::{
 
 /// Check for transaction mortality.
 ///
+/// The extension adds [`Era`] to every signed extrinsic. It also contributes to the signed data, by
+/// including the hash of the block at [`Era::birth`].
+///
 /// # Transaction Validity
 ///
 /// The extension affects `longevity` of the transaction according to the [`Era`] definition.

substrate/frame/transaction-payment/skip-feeless-payment/src/lib.rs

@@ -16,8 +16,8 @@
 //! # Skip Feeless Payment Pallet
 //!
 //! This pallet allows runtimes that include it to skip payment of transaction fees for
-//! dispatchables marked by [`#[pallet::feeless_if]`](`macro@
-//! frame_support::pallet_prelude::feeless_if`).
+//! dispatchables marked by
+//! [`#[pallet::feeless_if]`](frame_support::pallet_prelude::feeless_if).
 //!
 //! ## Overview
 //!
@@ -30,8 +30,9 @@
 //! ## Integration
 //!
 //! This pallet wraps an existing transaction payment pallet. This means you should both pallets
-//! in your `construct_runtime` macro and include this pallet's
-//! [`SignedExtension`] ([`SkipCheckIfFeeless`]) that would accept the existing one as an argument.
+//! in your [`construct_runtime`](frame_support::construct_runtime) macro and
+//! include this pallet's [`SignedExtension`] ([`SkipCheckIfFeeless`]) that would accept the
+//! existing one as an argument.
 
 #![cfg_attr(not(feature = "std"), no_std)]