Merge pull request #48 from CosmWasm/aw/events-corrections

Corrections of Cosmos Events

src/pages/core/architecture/events.mdx

@@ -2,13 +2,26 @@
 tags: ["core", "architecture"]
 ---
 
+import { Callout } from "nextra/components";
+
 # Events
 
 CosmWasm can emit
 [Cosmos Events](https://docs.cosmos.network/v0.50/learn/advanced/events). These
 events are stored in the block as metadata, allowing the contract to attach
 metadata to what exactly happened during execution.
 
+<Callout>
+
+Some important details about the keys:
+
+- Whitespaces will be trimmed (i.e.removed from the begin and end)
+- Empty keys (that includes keys only consisting of whitespaces) are not allowed
+- Keys _cannot_ start with an underscore (`_`). These types of keys are reserved
+  for `wasmd`
+
+</Callout>
+
 By default CosmWasm emits the `wasm` event to which you can add context like so:
 
 ```rust filename="wasm_event.rs" template="core"
@@ -22,6 +35,10 @@ As mentioned above, CosmWasm only emits the event `wasm` by default. If you want
 to emit other events, such as domain-specific events like `user_added`, you can
 construct a fully custom event and attach it to the response.
 
+<Callout>
+  Note that those custom events will be prefixed with `wasm-` by the runtime.
+</Callout>
+
 ```rust filename="custom_event.rs" template="core"
 let event = Event::new("custom_event")
     .add_attribute("custom_attribute", "value");