remove currencySystem member (#694)

* Remove `currencySystem` member
* Editorial: add note about digital currencies

Author: marcoscaceres

index.html

@@ -120,12 +120,6 @@ 
           before proceeding along the W3C Recommendation track.
         p>
         <ul>
-          <li>
-            <a data-lt=
-            "PaymentCurrencyAmount.currencySystem">currencySystema> (see
-            <a href="https://github.com/w3c/payment-request/issues/617">issue
-            617a>).
-          li>
           <li data-link-for="PaymentItem">
             <a>PaymentItema>'s <a>typea> member and the
             <a>PaymentItemTypea> enum (see <a href=
@@ -1407,56 +1401,63 @@ 
         dictionary PaymentCurrencyAmount {
           required DOMString currency;
           required DOMString value;
-          // Note: currencySystem is "at risk" of being removed!
-          DOMString currencySystem = "urn:iso:std:iso:4217";
         };
       pre>
       <p>
         A <a>PaymentCurrencyAmounta> dictionary is used to supply monetary
         amounts.
       p>
-      <div class="issue atrisk">
-        <p>
-          This feature has been marked "<a>at riska>". If you'd like for this
-          feature to remain in the specification, please describe your use case
-          in <a href="https://github.com/w3c/payment-request/issues/490">issue
-          490a>.
-        p>
-        <dl>
-          <dt>
-            <dfn>currencySystemdfn> member
-          dt>
-          <dd>
-            A URL that indicates the currency system that the <a>currencya>
-            identifier belongs to. By default, the value is
-            "<code>urn:iso:std:iso:4217code>" indicating that <a>currencya>
-            is defined by [[!ISO4217]] (for example, <code>USDcode> for US
-            Dollars).
-          dd>
-        dl>
-      div>
       <dl>
         <dt>
           <dfn>currencydfn> member
         dt>
         <dd>
           <p>
-            A string containing a currency identifier. The value of
-            <a>currencya> can be any string that is valid within the currency
-            system indicated by <a>currencySystema>.
-          p>
-          <p>
-            When using [[!ISO4217]], all <a data-cite=
+            A [[!ISO4217]] <a data-cite=
             "!ecma-402#sec-iswellformedcurrencycode">well-formeda> 3-letter
-            alphabetic codes are allowed (i.e., the numeric codes are not
-            supported). Their canonical form is upper case. However, the set of
-            combinations of currency code for which localized currency symbols
-            are available is implementation dependent. Where a localized
-            currency symbol is not available, a user agent SHOULD use U+00A4
-            (¤) for formatting. User agents MAY format the display of the
-            <a>currencya> member to adhere to OS conventions (e.g., for
-            localization purposes).
+            alphabetic code (i.e., the numeric codes are not supported). Their
+            canonical form is upper case. However, the set of combinations of
+            currency code for which localized currency symbols are available is
+            implementation dependent. Where a localized currency symbol is not
+            available, a user agent SHOULD use U+00A4 (¤) for formatting. User
+            agents MAY format the display of the <a>currencya> member to
+            adhere to OS conventions (e.g., for localization purposes).
           p>
+          <div class="note" title=
+          "Digital currencies and ISO 4217 currency codes">
+            <p>
+              User agents implementing this specification enforce [[ISO4217]]'s
+              3-letter codes format via ECMAScript’s <a data-cite=
+              "!ecma-402#sec-iswellformedcurrencycode">isWellFormedCurrencyCodea>
+              abstract operation, which is invoked as part of the <a>check and
+              canonicalize amounta> algorithm. When a code does not adhere to
+              the [[ISO4217]] defined format, a <a>RangeErrora> is thrown.
+            p>
+            <p>
+              Current implementations will therefore allow the use of
+              well-formed currency codes that are not part of the official
+              [[ISO4217]] list (e.g., XBT, XRP, etc.). If the provided code is
+              a currency that the browser knows how to display, then an
+              implementation will generally display the appropriate currency
+              symbol in the user interface (e.g., "USD" is shown as "$", "GBP"
+              is "£", and the non-standard "XBT" could be shown as "Ƀ"). When a
+              code cannot be matched, the specification recommends browsers
+              show a scarab "¤".
+            p>
+            <p>
+              Efforts are underway at ISO to account for digital currencies,
+              which may result in an update to the [[ISO4217]] registry or an
+              entirely new registry. The community expects this will resolve
+              ambiguities that have crept in through the use of non-standard
+              3-letter codes; for example, does "BTC" refer to Bitcoin or to a
+              future Bhutan currency? At the time of publication, it remains
+              unclear what form this evolution will take, or even the time
+              frame in which the work will be completed. The W3C Web Payments
+              Working Group is liaising with ISO so that, in the future,
+              revisions to this specification remain compatible with relevant
+              ISO registries.
+            p>
+          div>
         dd>
         <dt>
           <dfn>valuedfn> member
@@ -1506,11 +1507,6 @@ 
           steps:
         p>
         <ol data-link-for="PaymentCurrencyAmount">
-          <li data-tests=
-          "PaymentCurrencyAmount/currencySystem-member.https.html">If
-          <var>amountvar>.<a>currencySystema> is not
-          "<code>urn:iso:std:iso:4217code>", throw a <a>TypeErrora>.
-          li>
           <li>Let <var>isValidCurrencyvar> be the result of calling
           <a data-cite=
           "!ecma-402#sec-iswellformedcurrencycode">IsWellFormedCurrencyCodea>
@@ -1536,9 +1532,6 @@ 
           steps:
         p>
         <ol data-link-for="PaymentCurrencyAmount">
-          <li>If <var>totalvar>.<a>currencySystema> is not
-          "<code>urn:iso:std:iso:4217code>", terminate this algorithm.
-          li>
           <li>
             <a>Check and canonicalize amounta> <var>amountvar>. Rethrow any
             exceptions.