Merge pull request #3010 from XRPLF/2985_nft_txr_rules

Add note that NFTs with transfer fees require that the issuer has a trust line to the token used to buy the NFT

Author: DennisDawson

docs/concepts/tokens/nfts/index.md

@@ -28,7 +28,7 @@ NFTs have several immutable settings that are defined when the token is minted.
 - Identifying data that uniquely defines the token.
 - Whether the issuer can burn the token, regardless of who currently holds it.
 - Whether the holder of the token can transfer it to others. (An NFT can always be sent to or from the issuer directly.)
-- If transfers are allowed, the issuer can charge a transfer fee as a percentage of the sale price.
+- If transfers are allowed, the issuer can charge a transfer fee as a percentage of the sale price. If there is a transfer fee, the NFT can only be traded for tokens for which the issuer has a trust line.
 - Whether the holder can sell the NFT for [fungible token](../fungible-tokens/index.md) amounts, or only for XRP.
 
 ## NFT Lifecycle

docs/concepts/tokens/nfts/trading.md

@@ -19,6 +19,10 @@ Every `NFTokenOffer` object requires that your account increase its owner reserv
 
 See [NFT Reserve Requirements](reserve-requirements.md).
 
+## Transfer Fees
+
+As an issuer, you can mint your NFT with a transfer fee to be collected whenever your NFT is traded on the XRPL. If you specify a transfer fee, the NFT can only be traded for tokens for which you have a trust line. See [Trust Lines](../fungible-tokens/index.md#trust-lines).
+
 ## Sell Offers
 
 ### Create a Sell Offer

docs/tutorials/javascript/nfts/mint-and-burn-nfts.md

@@ -45,7 +45,7 @@ To mint a non-fungible token object:
 
 1. Set the **Flags** field. For testing purposes, we recommend setting the value to _8_. This sets the _tsTransferable_ flag, meaning that the NFT object can be transferred to another account. Otherwise, the NFT object can only be transferred back to the issuing account.
 2. Enter the **Token URL**. This is a URI that points to the data or metadata associated with the NFT object. You can use the sample URI provided if you do not have one of your own.
-3. Enter the **Transfer Fee**, a percentage of the proceeds from future sales of the NFT that will be returned to the original creator. This is a value of 0-50000 inclusive, allowing transfer rates between 0.000% and 50.000% in increments of 0.001%. If you do not set the **Flags** field to allow the NFT to be transferrable, set this field to 0.
+3. Enter the **Transfer Fee**, a percentage of the proceeds from future sales of the NFT that will be returned to the original creator. This is a value of 0-50000 inclusive, allowing transfer rates between 0.000% and 50.000% in increments of 0.001%. If you do not set the **Flags** field to allow the NFT to be transferrable, set this field to 0. If you impose a transfer fee, your NFT can only be traded for tokens for which your account has a trust line. See [Trust Lines](../../../concepts/tokens/fungible-tokens/index.md#trust-lines).
 4. Click **Mint NFT**.
 
 [![Mint NFT fields](/docs/img/quickstart10.png)](/docs/img/quickstart10.png)