From 75f8cf4b396debf20b6693df31b89a48cf3ea79e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marcos=20C=C3=A1ceres?= <mcaceres@mozilla.com>
Date: Thu, 31 Jan 2019 15:05:46 +1100
Subject: [PATCH] json parse, then convert

---
 index.html | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/index.html b/index.html
index 080c7b14..29a673cb 100644
--- a/index.html
+++ b/index.html
@@ -663,14 +663,31 @@ <h2>
                     <var>paymentMethod</var>.<a data-lt="PaymentMethodData.data">data</a>
                     into a string. Rethrow any exceptions.
                   </li>
-                  <li>If required by the specification that defines the
-                  <var>paymentMethod</var>.<a>supportedMethods</a>,
-                    <a data-lt="converting">convert</a>
-                    <var>paymentMethod</var>.<a>data</a> to an IDL value of the
-                    type specified there (e.g., a <a data-cite=
-                    "payment-method-basic-card#dom-basiccardrequest">BasicCardRequest</a>
-                    in the case of [[?payment-method-basic-card]]). Rethrow any
-                    exceptions.
+                  <li>If <var>serializedData</var> is not null, and if required
+                  by the specification that defines the
+                  <var>paymentMethod</var>.<a>supportedMethods</a>:
+                    <ol>
+                      <li>Let <var>object</var> be the result of
+                        <a data-cite="ECMASCRIPT#sec-json.parse">JSON-parsing</a>
+                        <var>serializedData</var>.
+                      </li>
+                      <li>
+                        <p>
+                          <a data-lt="converting">Convert</a> <var>object</var>
+                          to an IDL value of the type specified by the
+                          specification that defines the
+                          <var>paymentMethod</var>.<a>supportedMethods</a>
+                          (e.g., a <a data-cite=
+                          "payment-method-basic-card#dom-basiccardrequest">BasicCardRequest</a>
+                          in the case of [[?payment-method-basic-card]]).
+                          Rethrow any exceptions.
+                        </p>
+                        <p class="note">
+                          This step assures that any IDL type conversion errors
+                          are caught as early as possible.
+                        </p>
+                      </li>
+                    </ol>
                   </li>
                   <li>Add the tuple (<var>paymentMethod</var>.<a data-lt=
                   "PaymentMethodData.supportedMethods">supportedMethods</a>,