[spec] hex-escape punctuators

Fixes 65

spec.emu

@@ -15,26 +15,6 @@ contributors: Jordan Harband
   <emu-clause id="sec-regexp-regular-expression-objects" number="2">
     <h1>RegExp (Regular Expression) Objects</h1>
 
-    <emu-clause id="sec-patterns" number="1">
-      <h1>Patterns</h1>
-
-      <h2>Syntax</h2>
-      <p>Each `\\u` |HexTrailSurrogate| for which the choice of associated `u` |HexLeadSurrogate| is ambiguous shall be associated with the nearest possible `u` |HexLeadSurrogate| that would otherwise have no corresponding `\\u` |HexTrailSurrogate|.</p>
-      <emu-grammar type="definition">
-        HexNonSurrogate ::
-          Hex4Digits [> but only if the MV of |Hex4Digits| is not in the inclusive interval from 0xD800 to 0xDFFF]
-
-        IdentityEscape[UnicodeMode] ::
-          [+UnicodeMode] SyntaxCharacter
-          [+UnicodeMode] `/` <ins>`,` `-` `=` `<` `>` `#` `&` `!` `%` `:` `;` `@` `~` `'` `"` `\``</ins>
-          <ins>[+UnicodeMode] WhiteSpace</ins>
-          [~UnicodeMode] SourceCharacter but not UnicodeIDContinue
-
-        DecimalEscape ::
-          NonZeroDigit DecimalDigits[~Sep]? [lookahead &notin; DecimalDigit]
-      </emu-grammar>
-    </emu-clause>
-
     <emu-clause id="sec-properties-of-the-regexp-constructor" number="5">
       <h1>Properties of the RegExp Constructor</h1>
 
@@ -55,9 +35,14 @@ contributors: Jordan Harband
               1. Append code unit U+005C (REVERSE SOLIDUS) to _escapedList_.
               1. Append code unit U+0078 (LATIN SMALL LETTER X) to _escapedList_.
               1. Append code unit U+0033 (DIGIT THREE) to _escapedList_.
+              1. Append _c_ to _escapedList_.
             1. Else if _toEscape_ contains _c_ or _c_ is matched by |WhiteSpace|, then
               1. Append code unit U+005C (REVERSE SOLIDUS) to _escapedList_.
-            1. Append _c_ to _escapedList_.
+              1. Append code unit U+0078 (LATIN SMALL LETTER X) to _escapedList_.
+              1. Let _code_ be ℝ(! Call(%parseInt%, CodePointsToString(« _c_ »), « *16*<sub>𝔽</sub> »)) - 36.
+              1. Append the code unit whose numeric value is _code_ to _escapedList_.
+            1. Else,
+              1. Append _c_ to _escapedList_.
           1. Return CodePointsToString(_escapedList_).
         </emu-alg>