Update indexing-transactions.md (#4045)

* Update indexing-transactions.md

* Toml instead of Yaml

docs/app-dev/indexing-transactions.md

@@ -3,9 +3,18 @@
 Tendermint allows you to index transactions and later query or subscribe
 to their results.
 
+Events can be used to index transactions and blocks according to what happened
+during their execution. Note that the set of events returned for a block from
+`BeginBlock` and `EndBlock` are merged. In case both methods return the same
+tag, only the value defined in `EndBlock` is used.
+
+Each event contains a type and a list of attributes, which are key-value pairs
+denoting something about what happened during the method's execution. For more
+details on `Events`, see the [ABCI](../spec/abci/abci.md) documentation.
+
 Let's take a look at the `[tx_index]` config section:
 
-```
+```toml
 ##### transactions indexer configuration options #####
 [tx_index]
 
@@ -36,57 +45,61 @@ index_all_tags = false
 
 By default, Tendermint will index all transactions by their respective
 hashes using an embedded simple indexer. Note, we are planning to add
-more options in the future (e.g., Postgresql indexer).
+more options in the future (e.g., PostgreSQL indexer).
 
-## Adding tags
+## Adding Events
 
-In your application's `DeliverTx` method, add the `Tags` field with the
-pairs of UTF-8 encoded strings (e.g. "account.owner": "Bob", "balance":
-"100.0", "date": "2018-01-02").
+In your application's `DeliverTx` method, add the `Events` field with pairs of
+UTF-8 encoded strings (e.g. "transfer.sender": "Bob", "transfer.recipient": "Alice",
+"transfer.balance": "100").
 
 Example:
 
-```
+```go
 func (app *KVStoreApplication) DeliverTx(req types.RequestDeliverTx) types.Result {
-    ...
-    tags := []cmn.KVPair{
-      {[]byte("account.name"), []byte("igor")},
-      {[]byte("account.address"), []byte("0xdeadbeef")},
-      {[]byte("tx.amount"), []byte("7")},
+    //...
+    events := []abci.Event{
+        {
+            Type: "transfer",
+            Attributes: cmn.KVPairs{
+                cmn.KVPair{Key: []byte("sender"), Value: []byte("Bob")},
+                cmn.KVPair{Key: []byte("recipient"), Value: []byte("Alice")},
+                cmn.KVPair{Key: []byte("balance"), Value: []byte("100")},
+            },
+        },
     }
-    return types.ResponseDeliverTx{Code: code.CodeTypeOK, Tags: tags}
+    return types.ResponseDeliverTx{Code: code.CodeTypeOK, Events: events}
 }
 ```
 
-If you want Tendermint to only index transactions by "account.name" tag,
-in the config set `tx_index.index_tags="account.name"`. If you to index
-all tags, set `index_all_tags=true`
+If you want Tendermint to only index transactions by "transfer.sender" event type,
+in the config set `tx_index.index_tags="transfer.sender"`. If you to index all events,
+set `index_all_tags=true`
 
-Note, there are a few predefined tags:
+Note, there are a few predefined event types:
 
 - `tx.hash` (transaction's hash)
 - `tx.height` (height of the block transaction was committed in)
 
 Tendermint will throw a warning if you try to use any of the above keys.
 
-## Querying transactions
+## Querying Transactions
 
-You can query the transaction results by calling `/tx_search` RPC
-endpoint:
+You can query the transaction results by calling `/tx_search` RPC endpoint:
 
-```
+```shell
 curl "localhost:26657/tx_search?query=\"account.name='igor'\"&prove=true"
 ```
 
-Check out [API docs](https://tendermint.com/rpc/#txsearch)
-for more information on query syntax and other options.
+Check out [API docs](https://tendermint.com/rpc/#txsearch) for more information
+on query syntax and other options.
 
-## Subscribing to transactions
+## Subscribing to Transactions
 
-Clients can subscribe to transactions with the given tags via Websocket
-by providing a query to `/subscribe` RPC endpoint.
+Clients can subscribe to transactions with the given tags via Websocket by providing
+a query to `/subscribe` RPC endpoint.
 
-```
+```json
 {
     "jsonrpc": "2.0",
     "method": "subscribe",
@@ -97,5 +110,5 @@ by providing a query to `/subscribe` RPC endpoint.
 }
 ```
 
-Check out [API docs](https://tendermint.com/rpc/#subscribe) for
-more information on query syntax and other options.
+Check out [API docs](https://tendermint.com/rpc/#subscribe) for more information
+on query syntax and other options.