Move error type into behavioral category

Part of #463.

lang/spec.html

@@ -505,7 +505,7 @@ <h4>Type descriptors</h4>
 text items</td>
   </tr>
   <tr>
-   <td rowspan="6">basic, structured</td>
+   <td rowspan="5">basic, structured</td>
    <td>array</td>
    <td>an ordered list of values, optionally with a specific length, where a
 single type is specified for all members of the list</td>
@@ -530,12 +530,12 @@ <h4>Type descriptors</h4>
    <td>a two-dimensional collection of immutable values</td>
   </tr>
   <tr>
+   <td rowspan="8">basic, behavioral</td>
    <td>error</td>
    <td>an indication that there has been an error, with a string identifying the
 reason for the error, and a mapping giving additional details about the error</td>
   </tr>
   <tr>
-   <td rowspan="7">basic, behavioral</td>
    <td>function</td>
    <td>a function with 0 or more specified parameter types and a single return
 type</td>
@@ -1128,9 +1128,7 @@ <h5>XML namespaces</h5>
 <section>
 <h3>Structured values</h3>
 <p>
-There are four basic types of structured value. First, there are two container
-basic types: list and mapping. Second, there are the table and error basic
-types, which are each special in different ways.
+There are three basic types of structured value: list, mapping and table.
 </p>
 <p>
 A structured value is either mutable or immutable; whether it is mutable or
@@ -1177,7 +1175,6 @@ <h3>Structured values</h3>
    list-type-descriptor
    | mapping-type-descriptor
    | table-type-descriptor
-   | error-type-descriptor
 </pre>
 <p>
 The following table summarizes the type descriptors for structured types.
@@ -1547,6 +1544,22 @@ <h4>[Preview] Tables</h4>
 </p>
 
 </section>
+</section>
+<section>
+<h3>Behavioral values</h3>
+
+<pre
+class="grammar">behavioral-type-descriptor :=
+   error-type-descriptor
+   | function-type-descriptor
+   | object-type-descriptor
+   | future-type-descriptor
+   | service-type-descriptor
+   | typedesc-type-descriptor
+   | handle-type-descriptor
+   | stream-type-descriptor
+</pre>
+
 <section>
 <h4>Error</h4>
 
@@ -1559,10 +1572,9 @@ <h4>Error</h4>
 inferred-error-type-param := <code>*</code>
 </pre>
 <p>
-An error value belongs to the error basic type, which is a basic type which is
-distinct from other structured types and is used only for representing errors.
-The error type is inherently immutable. An error value contains the following
-information:
+An error value belongs to the error basic type, which is used only for
+representing errors. The error type is inherently immutable. An error value
+contains the following information:
 </p>
 <ul>
 <li>a reason, which is a string identifier for the category of error</li>
@@ -1617,21 +1629,6 @@ <h4>Error</h4>
 Error is the only structured basic type that is not iterable.
 </p>
 </section>
-</section>
-<section>
-<h3>Behavioral values</h3>
-
-<pre
-class="grammar">behavioral-type-descriptor :=
-   function-type-descriptor
-   | object-type-descriptor
-   | future-type-descriptor
-   | service-type-descriptor
-   | typedesc-type-descriptor
-   | handle-type-descriptor
-   | stream-type-descriptor
-</pre>
-
 
 <section>
 <h4 id="functions">Functions</h4>