Editorial: define the string types in terms of Infra types

Closes #335.

Author: jyasskin

index.bs

@@ -11,7 +11,9 @@ Complain About: accidental-2119 no
 </pre>
 
 <pre class="link-defaults">
-spec: infra; type: dfn; text: list
+spec: infra; type: dfn;
+    text: code unit
+    text: list
 spec: ecmascript; type: dfn;
     for: ECMAScript;
         text: constructor
@@ -2095,17 +2097,15 @@ the value is the IDL {{undefined}} value.
     1.  Depending on the type of the argument:
         <dl class="switch">
              :  {{DOMString}}
+             :  {{USVString}}
              :  an [=enumeration=] type
              :: The value of the <emu-t class="regex"><a href="#prod-string">string</a></emu-t> token
-                is the sequence of 16 bit unsigned integer code units
-                (hereafter referred to just as <dfn id="dfn-code-unit">code units</dfn>)
-                corresponding to the UTF-16 encoding of |S|.
+                is |S|.
              :  {{ByteString}}
-             :: The value of the <emu-t class="regex"><a href="#prod-string">string</a></emu-t> token
-                is the sequence of 8 bit unsigned integer code units
-                corresponding to the UTF-8 encoding of |S|.
-             :  {{USVString}}
-             :: The value of the <emu-t class="regex"><a href="#prod-string">string</a></emu-t> token is |S|.
+             :: Assert: |S| doesn't contain any [=code points=] higher than U+00FF.
+
+                The value of the <emu-t class="regex"><a href="#prod-string">string</a></emu-t> token
+                is the [=isomorphic encoding=] of |S|.
         </dl>
 </div>
 
@@ -5436,7 +5436,8 @@ allows authors to register callbacks by providing objects that implement the
 
 <h3 id="idl-types">Types</h3>
 
-This section lists the types supported by Web IDL, the set of values
+This section lists the types supported by Web IDL,
+the set of values or [[Infra|Infra]] type
 corresponding to each type, and how [=constants=]
 of that type are represented.
 
@@ -5791,10 +5792,7 @@ The {{bigint}} type is an arbitrary integer type, unrestricted in range.
 
 <h4 oldids="dom-DOMString" id="idl-DOMString" interface>DOMString</h4>
 
-The {{DOMString}} type corresponds to
-the set of all possible sequences of [=code units=].
-Such sequences are commonly interpreted as UTF-16 encoded strings [[!RFC2781]]
-although this is not required.
+The {{DOMString}} type corresponds to [=strings=].
 
 Note: Note also that <emu-val>null</emu-val>
 is not a value of type {{DOMString}}.
@@ -5818,7 +5816,7 @@ can be set to [=value of string literal tokens|the value=] of a
 <h4 oldids="dom-ByteString" id="idl-ByteString" interface>ByteString</h4>
 
 The {{ByteString}} type
-corresponds to the set of all possible sequences of bytes.
+corresponds to [=byte sequences=].
 Such sequences might be interpreted as UTF-8 encoded strings [[!RFC3629]]
 or strings in some other 8-bit-per-code-unit encoding, although this is not required.
 
@@ -5845,10 +5843,10 @@ can be set to [=value of string literal tokens|the value=] of a
 <h4 oldids="dom-USVString" id="idl-USVString" interface>USVString</h4>
 
 The {{USVString}} type
-corresponds to the set of all possible sequences of
-[=scalar values=],
-which are all of the Unicode code points apart from the
-surrogate code points.
+corresponds to [=scalar value strings=].
+Depending on the context,
+these can be treated as sequences of either 16-bit unsigned integer [=code units=]
+or [=scalar values=].
 
 There is no way to represent a constant {{USVString}}
 value in IDL, although {{USVString}} [=dictionary member=] [=dictionary member/default values=]
@@ -7471,12 +7469,9 @@ value when its bit pattern is interpreted as an unsigned 64 bit integer.
 
 <div id="USVString-to-es" algorithm="convert an USVString to an ECMAScript value">
 
-    An IDL {{USVString}} value is [=converted to an ECMAScript value|converted=]
-    to an ECMAScript value by running the following algorithm:
-
-    1.  Let |scalarValues| be the sequence of [=scalar values=] the {{USVString}} represents.
-    1.  Let |string| be the sequence of [=code units=] that results from encoding |scalarValues| in UTF-16.
-    1.  Return the String value that represents the same sequence of [=code units=] as |string|.
+    The result of [=converted to an ECMAScript value|converting=]
+    an IDL {{USVString}} value |S| to an ECMAScript
+    value is |S|.
 </div>