CH02::getting inputs: warn about privacy for address lookup calls

ch02.asciidoc

@@ -50,6 +50,8 @@ information from the Bitcoin network. With each transaction or block
 example, we will provide a URL so you can look it up yourself and study
 it in detail.
 
+[[block-explorer-privacy]]
+.Block explorer privacy warning
 [WARNING]
 ====
 Searching information on a block explorer may disclose to its operator
@@ -354,15 +356,18 @@ However, because full nodes use more resources, most
 user wallets run "lightweight" clients that track only the user's own
 UTXOs.
 
-If the wallet application does not maintain a copy of unspent
-transaction outputs, it can query the Bitcoin network to retrieve this
+If the wallet application does not maintain a copy of all UTXOs, it can
+query the Bitcoin network to retrieve this
 information using a variety of APIs available by different providers or
-by asking a full-node using an application programming interface (API)
+by asking a full node using an application programming interface (API)
 call. <<example_2-2>> shows an API request, constructed as an HTTP GET
 command to a specific URL. This URL will return all the unspent
 transaction outputs for an address, giving any application the
 information it needs to construct transaction inputs for spending. We
 use the simple command-line HTTP client _cURL_ to retrieve the response.
+Note that looking up information using a third-party API like this is similar to
+using a block explorer; see the privacy warning in
+<<block-explorer-privacy>>.
 
 [[example_2-2]]
 .Look up all the unspent outputs for Alice's Bitcoin address