Merge pull request #382 from stellar/msfeldstein-patch-4

[SEP6] Show example postMessage syntax

ecosystem/sep-0006.md

@@ -378,6 +378,22 @@ If the wallet wants to be notified that the user has completed the anchor's inte
 
 In either case, the JSON message should be identical to the response format for the [/transaction](#single-historical-transaction) endpoint.
 
+```javascript
+// Example postMessage callback at the end of an interactive withdraw, indicating that the anchor is waiting for the wallet to send a payment in the amount of 80 of the asset in question. 
+const target = window.opener || window.parent;
+target.postMessage({
+ transaction: {
+   id: "anchors_identifier_for_this_transaction",
+   status: "pending_user_transfer_start",
+   withdraw_anchor_account: "ANCHORS_STELLAR_ACCOUNT_ID",
+   withdraw_memo: "MEMO_ANCHOR_EXPECTS_TO_SEE",
+   withdraw_memo_type: "text|hash|id",
+   amount_in: "80"
+   // ... Any other values from the /transaction endpoint may be passed as well
+ }
+}, "*");
+```
+
 As an alternative to using the `callback` parameter, the wallet can poll the transaction endpoint [`/transaction`](#single-historical-transaction) with the request `id` to check the status of the request.
 
 **`jwt` details**