Doc: fix minor issues in GiST support function documentation.

gist.sgml and xindex.sgml hadn't been fully updated for the
addition of a sortsupport support function (commit 16fa9b2b3).
xindex.sgml also missed that the compress and decompress support
functions are optional, an apparently far older oversight.

In passing, fix gratuitous inconsistencies in wording and
capitalization.

Noted by E. Rogov.  Back-patch to v14; the residual issues
before that aren't significant enough to bother with.

Discussion: https://postgr.es/m/163335322905.12519.5711557029494638051@wrigleys.postgresql.org

doc/src/sgml/gist.sgml

@@ -272,7 +272,7 @@ CREATE INDEX ON my_table USING GIST (my_inet_column inet_ops);
 
  <para>
    There are five methods that an index operator class for
-   <acronym>GiST</acronym> must provide, and five that are optional.
+   <acronym>GiST</acronym> must provide, and six that are optional.
    Correctness of the index is ensured
    by proper implementation of the <function>same</function>, <function>consistent</function>
    and <function>union</function> methods, while efficiency (size and speed) of the
@@ -291,9 +291,9 @@ CREATE INDEX ON my_table USING GIST (my_inet_column inet_ops);
    searches). The optional ninth method <function>fetch</function> is needed if the
    operator class wishes to support index-only scans, except when the
    <function>compress</function> method is omitted. The optional tenth method
-   <function>options</function> is needed if the operator class provides
+   <function>options</function> is needed if the operator class has
-   the user-specified parameters.
+   user-specified parameters.
-   The <function>sortsupport</function> method is also optional and is used to
+   The optional eleventh method <function>sortsupport</function> is used to
    speed up building a <acronym>GiST</acronym> index.
  </para>
 

doc/src/sgml/xindex.sgml

@@ -459,7 +459,7 @@
       </row>
       <row>
        <entry>
-        Defines a set of options that are specific to this operator class
+        Define options that are specific to this operator class
         (optional)
        </entry>
        <entry>5</entry>
@@ -501,7 +501,7 @@
       </row>
       <row>
        <entry>
-        Defines a set of options that are specific to this operator class
+        Define options that are specific to this operator class
         (optional)
        </entry>
        <entry>3</entry>
@@ -511,7 +511,7 @@
    </table>
 
   <para>
-   GiST indexes have ten support functions, three of which are optional,
+   GiST indexes have eleven support functions, six of which are optional,
    as shown in <xref linkend="xindex-gist-support-table"/>.
    (For more information see <xref linkend="gist"/>.)
   </para>
@@ -544,13 +544,13 @@
       <row>
        <entry><function>compress</function></entry>
        <entry>compute a compressed representation of a key or value
-        to be indexed</entry>
+        to be indexed (optional)</entry>
        <entry>3</entry>
       </row>
       <row>
        <entry><function>decompress</function></entry>
        <entry>compute a decompressed representation of a
-        compressed key</entry>
+        compressed key (optional)</entry>
        <entry>4</entry>
       </row>
       <row>
@@ -566,7 +566,7 @@
        <entry>6</entry>
       </row>
       <row>
-       <entry><function>equal</function></entry>
+       <entry><function>same</function></entry>
        <entry>compare two keys and return true if they are equal</entry>
        <entry>7</entry>
       </row>
@@ -583,12 +583,16 @@
       </row>
       <row>
        <entry><function>options</function></entry>
-       <entry>
+       <entry>define options that are specific to this operator class
-        Defines a set of options that are specific to this operator class
+        (optional)</entry>
-        (optional)
-       </entry>
        <entry>10</entry>
       </row>
+      <row>
+       <entry><function>sortsupport</function></entry>
+       <entry>provide a sort comparator to be used in fast index builds
+        (optional)</entry>
+       <entry>11</entry>
+      </row>
      </tbody>
     </tgroup>
    </table>
@@ -642,10 +646,8 @@
       </row>
       <row>
        <entry><function>options</function></entry>
-       <entry>
+       <entry>define options that are specific to this operator class
-        Defines a set of options that are specific to this operator class
+        (optional)</entry>
-        (optional)
-       </entry>
        <entry>6</entry>
       </row>
      </tbody>
@@ -720,7 +722,7 @@
       <row>
        <entry><function>options</function></entry>
        <entry>
-        Defines a set of options that are specific to this operator class
+        define options that are specific to this operator class
         (optional)
        </entry>
        <entry>7</entry>
@@ -778,7 +780,7 @@
       <row>
        <entry><function>options</function></entry>
        <entry>
-        Defines a set of options that are specific to this operator class
+        define options that are specific to this operator class
         (optional)
        </entry>
        <entry>5</entry>