Update walkthrough.md
Typos minor fix. Including suggestions on template parameters.
@@ -164,7 +164,7 @@ Asset Opt-In is a common operation for serveral use-cases based on Stateless
ASC1.
This example shows how to Opt-In an ASA with a Contract Account adopting
-security cheks to ensure that malicious users can not exploit Opt-In
+security chekcs to ensure that malicious users can not exploit Opt-In
transaction approval.
## Opt-In ASC1 TEAL logic
@@ -229,6 +229,15 @@ int VAR_TMPL_OPTIN_EXPIRING_BLOCK
b end_program
```
+For sake of generality the Contract Account ASA Opt-In example makes use of **template parameters**, that should be assigned according to the specific use case. In particular, before compiling the TEAL source code, the following parameters hardcoded into TEAL program should be assigned:
+
+1. `VAR_TMPL_ASSET_ID`: is the Asset ID of the ASA the Contract Account will Opt-In. This implies that the ASA must be created before the ASC1.
+2. `VAR_TMPL_OPTIN_FEE`: is the maximum [fee](https://developer.algorand.org/docs/features/transactions/#fees), expressed in microALGO, that the Contract Account would accept for the ASA Opt-In transaction. This check prevents malicious adversaries form forcing the Contract Account to pay arbitrarily high fees.
+3. `VAR_TMPL_OPTIN_EXPIRING_BLOCK`: setting a [last valid block](https://developer.algorand.org/docs/features/transactions/#setting-first-and-last-valid) for the ASA Opt-In transaction means that Contract Account will only approve ASA Opt-In transactions until a certain block. This check prevents malicious adversaries from draining Contract Account ALGOs in Opt-In transaction fees after that block.
+
+!!! tip
+ For [AlgoDea](https://algodea-docs.bloxbean.com/) users is convenient to adopt the prefix `VAR_TMPL_` as parameters naming convention so that they can be easily assigned directly within the IDE, before compiling the TEAL stateless program.
+
## Opt-In ASC1 depolyment
We get the Contract Address by compiling its TEAL logic:
@@ -262,4 +271,4 @@ goal clerk sign -i optin.txn -p contract.teal -o optin.stxn
goal clerk rawsend -f optin.stxn
```
-Then you can add more fund to the Contract Address once the Opt-In validity block expires.
+Then you can add more funds to the Contract Address once the Opt-In validity block expires.
