Contract: ERC721.sol

333:     function _transfer(address from, address to, uint256 tokenId) internal virtual {
334:         require(ERC721.ownerOf(tokenId) == from, "ERC721: transfer from incorrect owner");
335:         require(to != address(0), "ERC721: transfer to the zero address");
336: 
337:         _beforeTokenTransfer(from, to, tokenId, 1);
338: 
339:         // Check that tokenId was not transferred by `_beforeTokenTransfer` hook
340:         require(ERC721.ownerOf(tokenId) == from, "ERC721: transfer from incorrect owner");
341: 
342:         // Clear approvals from the previous owner
343:   >>    delete _tokenApprovals[tokenId];
344: 
345:         unchecked {
346:             // `_balances[from]` cannot overflow for the same reason as described in `_burn`:
347:             // `from`'s balance is the number of token held, which is at least one before the current
348:             // transfer.
349:             // `_balances[to]` could overflow in the conditions described in `_mint`. That would require
350:             // all 2**256 token ids to be minted, which in practice is impossible.
351:             _balances[from] -= 1;
352:             _balances[to] += 1;
353:         }
354:         _owners[tokenId] = to;
355: 
356:         emit Transfer(from, to, tokenId);
357: 
358:         _afterTokenTransfer(from, to, tokenId, 1);
359:     }
Contract: NonfungiblePositionManager.sol

183:     modifier isAuthorizedForToken(uint256 tokenId) {
184:         require(_isApprovedOrOwner(msg.sender, tokenId), 'Not approved');
185:         _;
186:     }
