Replace previous normalized device identifiers definition with a rail…

…road diagram

spec/index.bs

@@ -1486,21 +1486,21 @@ interface GPUAdapterInfo {
     1. Let |unmaskedValues| be |adapter|.{{adapter/[[unmaskedIdentifiers]]}}
     1. If |unmaskedValues| [=set/contains=] `"vendor"` and the vendor is known:
         1. Set |adapterInfo|.{{GPUAdapterInfo/vendor}} to the name of |adapter|'s vendor as a
-            [$normalized identifier string$].
+            [=normalized identifier string=].
 
         Otherwise:
 
         1. Set |adapterInfo|.{{GPUAdapterInfo/vendor}} to the empty string or a
-            reasonable approximation of the vendor as a [$normalized identifier string$].
+            reasonable approximation of the vendor as a [=normalized identifier string=].
 
     1. If |unmaskedValues| [=set/contains=] `"architecture"` and the architecture is known:
-        1. Set |adapterInfo|.{{GPUAdapterInfo/architecture}} to a [$normalized identifier string$]
+        1. Set |adapterInfo|.{{GPUAdapterInfo/architecture}} to a [=normalized identifier string=]
             representing the family or class of adapters to which |adapter| belongs.
 
         Otherwise:
 
         1. Set |adapterInfo|.{{GPUAdapterInfo/architecture}} to the empty string or a
-            reasonable approximation of the architecture as a [$normalized identifier string$].
+            reasonable approximation of the architecture as a [=normalized identifier string=].
 
     1. If |unmaskedValues| [=set/contains=] `"deviceId"` and the deviceId is known:
         1. Set |adapterInfo|.{{GPUAdapterInfo/deviceId}} to a vendor-specific numeric ID for
@@ -1524,14 +1524,22 @@ interface GPUAdapterInfo {
 </div>
 
 <div algorithm>
-    To generate a <dfn abstract-op>normalized identifier string</dfn> for a given {{DOMString}}
-    |identifier|, run the following steps:
-
-    1. Let |normalized| be a copy of |identifier|.
-    1. Remove any non-ASCII characters from |normalized|.
-    1. Convert |normalized| to lowercase.
-    1. Replace any spaces in |normalized| with a hyphen character. (`"-"`)
-    1. Return |normalized|.
+    A <dfn>normalized identifier string</dfn> is one that follows the following pattern:
+
+    <pre class='railroad'>
+    OneOrMore:
+        OneOrMore:
+            T: a-z 0-9
+        T: -
+    </pre>
+
+    <div class="example">
+    Examples of valid normalized identifier strings include:
+        - `gpu`
+        - `3d`
+        - `next-gen`
+        - `series-x20-ultra`
+    </div>
 </div>
 
 ## Origin Restrictions ## {#origin-restrictions}