Validate PMIs, ignore duplicates

* Validate supportedMethods (closes #464)
* Defines behavior for duplicate PMIs in contructor and updateWith() (closes #309)

index.html

@@ -566,8 +566,33 @@ <h2>
               then <a>throw</a> a <a>TypeError</a>, optionally informing the
               developer that at least one <a>payment method</a> is required.
               </li>
+              <li>Let <var>seenPMIs</var> be an emtpy list.
+              </li>
               <li>For each <var>paymentMethod</var> of <var>methodData</var>:
                 <ol>
+                  <li>Run the steps to <a data-cite=
+                  "payment-method-id#dfn-validate-a-payment-method-identifier">
+                    validate a payment method identifier</a> with
+                    <var>paymentMethod</var>.<a data-lt=
+                    "PaymentMethodData.supportedMethods">supportedMethods</a>.
+                    If it returns false, then throw a <a>RangeError</a>
+                    exception and terminate this algorithm. Optionally, inform
+                    the developer that the payment method identifier is
+                    invalid.
+                  </li>
+                  <li>If <a>seenPMIs</a> contains
+                  <var>paymentMethod</var>.<a data-lt=
+                  "PaymentMethodData.supportedMethods">supportedMethods</a>,
+                  continue to the next <var>paymentMethod</var> of
+                  <var>methodData</var> (if any). Optionally, inform the
+                  developer that <var>paymentMethod</var>.<a data-lt=
+                  "PaymentMethodData.supportedMethods">supportedMethods</a> was
+                  already seen and <var>paymentMethod</var> will be ignored.
+                  </li>
+                  <li>Append <var>paymentMethod</var>.<a data-lt=
+                  "PaymentMethodData.supportedMethods">supportedMethods</a> to
+                  <var>seenPMI</var>.
+                  </li>
                   <li>If the <a data-lt="PaymentMethodData.data">data</a>
                   member of <var>paymentMethod</var> is missing, let
                   <var>serializedData</var> be null. Otherwise, let
@@ -2547,9 +2572,21 @@ <h2>
                         <li>Let <var>serializedModifierData</var> be an empty
                         list.
                         </li>
+                        <li>Let <var>seenPMIs</var> be an empty list.
+                        </li>
                         <li>For each <a>PaymentDetailsModifier</a>
                         <var>modifier</var> in <var>modifiers</var>:
                           <ol data-link-for="PaymentDetailsModifier">
+                            <li>Run the steps to <a data-cite=
+                            "payment-method-id#dfn-validate-a-payment-method-identifier">
+                              validate a payment method identifier</a> with
+                              <var>modifier</var>.<a data-lt=
+                              "PaymentDetailsModifier.supportedMethods">supportedMethods</a>.
+                              If it returns false, then <a>abort the update</a>
+                              with a <a>RangeError</a> exception. Optional,
+                              inform the developer that the payment method
+                              identifier is invalid.
+                            </li>
                             <li>If the <a>total</a> member of
                             <var>modifier</var> is present, then:
                               <ol>
@@ -2588,6 +2625,20 @@ <h2>
                             exception, then <a>abort the update</a> with that
                             exception.
                             </li>
+                            <li>If <a>seenPMIs</a> contains
+                            <var>modifier</var>.<a data-lt=
+                            "PaymentDetailsModifier.supportedMethods">supportedMethods</a>,
+                            continue to the next <var>modifier</var> of
+                            <var>modifiers</var> (if any). Optionally, inform
+                            the developer that
+                              <var>modifier</var>.<a data-lt="PaymentDetailsModifier.supportedMethods">supportedMethods</a>
+                              was already seen and <var>modifier</var> will be
+                              ignored.
+                            </li>
+                            <li>Append <var>modifier</var>.<a data-lt=
+                            "PaymentDetailsModifier.supportedMethods">supportedMethods</a>
+                            to <var>seenPMI</var>.
+                            </li>
                             <li>Add <var>serializedData</var> to
                             <var>serializedModifierData</var>.
                             </li>