Editorial: Split 'Patterns' clause into two clauses

... namely
    Syntax for Patterns
and
    Static Semantics for Patterns

And for consistency, rename
    Pattern Semantics
to
    Runtime Semantics for Patterns

... so that clause-headers more precisely convey what content is where.

spec.html

@@ -33135,8 +33135,8 @@ <h1>RegExp (Regular Expression) Objects</h1>
     </emu-note>
 
     <emu-clause id="sec-patterns">
-      <h1>Patterns</h1>
-      <p>The RegExp constructor applies the following grammar to the input pattern String. An error occurs if the grammar cannot interpret the String as an expansion of |Pattern|.</p>
+      <h1>Syntax for Patterns</h1>
+      <p>The `RegExp` constructor applies the following grammar to the input pattern String. An error occurs if the grammar cannot interpret the String as an expansion of |Pattern|.</p>
       <h2>Syntax</h2>
       <emu-grammar type="definition">
         Pattern[U, N] ::
@@ -33340,6 +33340,10 @@ <h2>Syntax</h2>
           CharacterClassEscape[?U]
           CharacterEscape[?U]
       </emu-grammar>
+    </emu-clause>
+
+    <emu-clause id="sec-static-semantics-for-patterns">
+      <h1>Static Semantics for Patterns</h1>
 
       <emu-note>
         <p>A number of productions in this section are given alternative definitions in section <emu-xref href="#sec-regular-expressions-patterns"></emu-xref>.</p>
@@ -33697,10 +33701,7 @@ <h1>Static Semantics: CapturingGroupName</h1>
     </emu-clause>
 
     <emu-clause id="sec-pattern-semantics">
-      <h1>Pattern Semantics</h1>
-      <emu-note>
-        <p>This section is amended in <emu-xref href="#sec-regular-expression-patterns-semantics"></emu-xref>.</p>
-      </emu-note>
+      <h1>Runtime Semantics for Patterns</h1>
       <p>A regular expression pattern is converted into an Abstract Closure using the process described below. An implementation is encouraged to use more efficient algorithms than the ones listed below, as long as the results are the same. The Abstract Closure is used as the value of a RegExp object's [[RegExpMatcher]] internal slot.</p>
       <p>A |Pattern| is either a BMP pattern or a Unicode pattern depending upon whether or not its associated flags contain a `u`. A BMP pattern matches against a String interpreted as consisting of a sequence of 16-bit values that are Unicode code points in the range of the Basic Multilingual Plane. A Unicode pattern matches against a String interpreted as consisting of Unicode code points encoded using UTF-16. In the context of describing the behaviour of a BMP pattern &ldquo;character&rdquo; means a single 16-bit Unicode BMP code point. In the context of describing the behaviour of a Unicode pattern &ldquo;character&rdquo; means a UTF-16 encoded code point (<emu-xref href="#sec-ecmascript-language-types-string-type"></emu-xref>). In either context, &ldquo;character value&rdquo; means the numeric value of the corresponding non-encoded code point.</p>
       <p>The syntax and semantics of |Pattern| is defined as if the source code for the |Pattern| was a List of |SourceCharacter| values where each |SourceCharacter| corresponds to a Unicode code point. If a BMP pattern contains a non-BMP |SourceCharacter| the entire pattern is encoded using UTF-16 and the individual code units of that encoding are used as the elements of the List.</p>