Explanation of the difference between request `parameters` vs. `data`

Based on the response from @tanner in slack channel

routing/parameters.md

@@ -20,11 +20,11 @@ This creates a route that matches `users/:id` where the `:id` is an `Int`. Here'
 
 ```swift
 drop.get("users", ":id") { request in
-	guard let userId = request.parameters["id"].int else {
-		throw Abort.badRequest
-	}
+  guard let userId = request.parameters["id"].int else {
+    throw Abort.badRequest
+  }
 
-	return "You requested User #\(userId)"
+  return "You requested User #\(userId)"
 }
 ```
 
@@ -44,7 +44,7 @@ Our previous example with users can be further simplified.
 
 ```swift
 drop.get("users", User.self) { request, user in
-	return "You requested \(user.name)"
+  return "You requested \(user.name)"
 }
 ```
 
@@ -54,9 +54,9 @@ Here is what this would look like if model didn't conform to `StringInitializabl
 
 ```swift
 drop.get("users", Int.self) { request, userId in
-	guard let user = try User.find(userId) else {
-		throw Abort.notFound
-	}
+  guard let user = try User.find(userId) else {
+    throw Abort.notFound
+  }
 
     return "You requested User #\(userId)"
 }
@@ -96,9 +96,9 @@ Type safe routing is currently limited to three path parts. This is usually reme
 
 ```swift
 drop.group("v1", "users") { users in
-	users.get(User.self, "posts", Post.self) { request, user, post in
-		return "Requested \(post.name) for \(user.name)"
-	}
+  users.get(User.self, "posts", Post.self) { request, user, post in
+    return "Requested \(post.name) for \(user.name)"
+  }
 }
 ```
 
@@ -110,14 +110,16 @@ As shown briefly above, you are still free to do traditional routing. This can b
 
 ```swift
 drop.get("v1", "users", ":userId", "posts", ":postId", "comments": ":commentId") { request in
-	let userId = try request.parameters.extract("userId") as Int
-	let postId = try request.parameters.extract("postId") as Int
-	let commentId = try request.parameters.extract("commentId") as Int
+  let userId = try request.parameters.extract("userId") as Int
+  let postId = try request.parameters.extract("postId") as Int
+  let commentId = try request.parameters.extract("commentId") as Int
 
-	return "You requested comment #\(commentId) for post #\(postId) for user #\(userId)"
+  return "You requested comment #\(commentId) for post #\(postId) for user #\(userId)"
 }
 ```
 
+> Property `request.parameters` is used to extract parameters encoded in the URI _path_ (for example, `/v1/users/1` has a parameter `:userId` equal to `"1"`). In case of parameters passed as a part of a _query_ (e.g. `/v1/search-user?userId=1`), the `request.data` should be used (e.g. `let userId = request.data["userId"]?.string`).
+
 Request parameters can be accessed either as a dictionary or using the `extract` syntax which throws instead of returning an optional.
 
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