docs: describe B20's externally observable architecture (base-std@0207138)

Co-authored-by: Toshi <toshi-noreply@coinbase.com>

Author: soheimam

docs/build-on-base/issue-rwa/create-an-asset-token.mdx

@@ -73,7 +73,7 @@ export async function createStockToken() {
 ```
 </CodeGroup>
 
-The factory assigns a deterministic address from `(variant, sender, salt)`. Address byte `[10]` is `0x00` for Asset tokens. Reusing the same `(variant, sender, salt)` triple reverts `TokenAlreadyExists`. Optional `initCalls`, such as the role grants above, run on the new token in the same transaction. The factory drops access after `createB20` returns.
+The factory assigns a deterministic address from `(variant, sender, salt)`. Address byte `[10]` selects which selectors that address accepts — `0x00` for Asset tokens. Reusing the same `(variant, sender, salt)` triple reverts `TokenAlreadyExists`. Optional `initCalls`, such as the role grants above, run on the new token in the same transaction. The factory drops access after `createB20` returns.
 
 See the [B20 token standard](/build-on-base/issue-rwa/create-an-asset-token) for the complete interface, roles, and policies.