[fix lint warnings: NFTs pallet] fix clippy::missing_docs_in_private_items warnings (#14610)

* add docs for impl_codec_bitflags

* add missing docs for type aliases

* add docs to transfer module

* add docs for settings module

* add docs to roles module

* add docs to metadata module

* add docs to migration module

* add missing docs to feature library

* methods not functions

* add docs to lock module

* add docs to attributes module

* add docs to create_delete_item module

* add docs for create_delete_collection module

* add docs to buy_sell module

* add missing doc for buy_sell module

* add docs to atomic_swap module

* add docs to atomic_swap module

* add docs for approvals module

* run cargo fmt

* Fix issues with multi-line comments

* Apply suggestions from code review

Co-authored-by: Jegor Sidorenko <5252494+jsidorenko@users.noreply.github.com>

* update from review

* fmt

* update from review

* remove bitflag example

* ".git/.scripts/commands/fmt/fmt.sh"

* Apply suggestions from code review

Co-authored-by: Squirrel <gilescope@gmail.com>

* add note about pallet features

---------

Co-authored-by: Jegor Sidorenko <jegor@parity.io>
Co-authored-by: Jegor Sidorenko <5252494+jsidorenko@users.noreply.github.com>
Co-authored-by: parity-processbot <>
Co-authored-by: Squirrel <gilescope@gmail.com>

substrate/frame/nfts/src/features/approvals.rs

@@ -15,10 +15,32 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//! This module contains helper functions for the approval logic implemented in the NFTs pallet.
+//! The bitflag [`PalletFeature::Approvals`] needs to be set in [`Config::Features`] for NFTs
+//! to have the functionality defined in this module.
+
 use crate::*;
 use frame_support::pallet_prelude::*;
 
 impl<T: Config<I>, I: 'static> Pallet<T, I> {
+	/// Approves the transfer of an item to a delegate.
+	///
+	/// This function is used to approve the transfer of the specified `item` in the `collection` to
+	/// a `delegate`. If `maybe_check_origin` is specified, the function ensures that the
+	/// `check_origin` account is the owner of the item, granting them permission to approve the
+	/// transfer. The `delegate` is the account that will be allowed to take control of the item.
+	/// Optionally, a `deadline` can be specified to set a time limit for the approval. The
+	/// `deadline` is expressed in block numbers and is added to the current block number to
+	/// determine the absolute deadline for the approval. After approving the transfer, the function
+	/// emits the `TransferApproved` event.
+	///
+	/// - `maybe_check_origin`: The optional account that is required to be the owner of the item,
+	///   granting permission to approve the transfer. If `None`, no permission check is performed.
+	/// - `collection`: The identifier of the collection containing the item to be transferred.
+	/// - `item`: The identifier of the item to be transferred.
+	/// - `delegate`: The account that will be allowed to take control of the item.
+	/// - `maybe_deadline`: The optional deadline (in block numbers) specifying the time limit for
+	///   the approval.
 	pub(crate) fn do_approve_transfer(
 		maybe_check_origin: Option<T::AccountId>,
 		collection: T::CollectionId,
@@ -63,6 +85,20 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 		Ok(())
 	}
 
+	/// Cancels the approval for the transfer of an item to a delegate.
+	///
+	/// This function is used to cancel the approval for the transfer of the specified `item` in the
+	/// `collection` to a `delegate`. If `maybe_check_origin` is specified, the function ensures
+	/// that the `check_origin` account is the owner of the item or that the approval is past its
+	/// deadline, granting permission to cancel the approval. After canceling the approval, the
+	/// function emits the `ApprovalCancelled` event.
+	///
+	/// - `maybe_check_origin`: The optional account that is required to be the owner of the item or
+	///   that the approval is past its deadline, granting permission to cancel the approval. If
+	///   `None`, no permission check is performed.
+	/// - `collection`: The identifier of the collection containing the item.
+	/// - `item`: The identifier of the item.
+	/// - `delegate`: The account that was previously allowed to take control of the item.
 	pub(crate) fn do_cancel_approval(
 		maybe_check_origin: Option<T::AccountId>,
 		collection: T::CollectionId,
@@ -100,6 +136,19 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 		Ok(())
 	}
 
+	/// Clears all transfer approvals for an item.
+	///
+	/// This function is used to clear all transfer approvals for the specified `item` in the
+	/// `collection`. If `maybe_check_origin` is specified, the function ensures that the
+	/// `check_origin` account is the owner of the item, granting permission to clear all transfer
+	/// approvals. After clearing all approvals, the function emits the `AllApprovalsCancelled`
+	/// event.
+	///
+	/// - `maybe_check_origin`: The optional account that is required to be the owner of the item,
+	///   granting permission to clear all transfer approvals. If `None`, no permission check is
+	///   performed.
+	/// - `collection`: The collection ID containing the item.
+	/// - `item`: The item ID for which transfer approvals will be cleared.
 	pub(crate) fn do_clear_all_transfer_approvals(
 		maybe_check_origin: Option<T::AccountId>,
 		collection: T::CollectionId,