DOC: typo and style fixes for knn docs

Author: Liudmila Mantrova

doc/src/sgml/indices.sgml

@@ -1493,7 +1493,7 @@ are index columns of the multicolumn GiST index.
     You can run <acronym>k-NN</acronym> search for all built-in and
     custom data types that support the concept of distance. In database 
     queries, k-NN search can provide performance benefits for 
-    various use cases: georgraphic information systems (<acronym>GIS</acronym>),
+    various use cases: geographic information systems (<acronym>GIS</acronym>),
     classification problems (majority voting), clusterization,
     looking for similar objects or nearest events, detecting 
     duplications and typos, trigram matching, multimedia search, and more.
@@ -1520,9 +1520,9 @@ are index columns of the multicolumn GiST index.
     the tuple entry is used. In the tree nodes, leaf nodes are stored before the 
     inner nodes in the list, so tuple entries are processed first. Each time
     a result is returned from the queue, it is guaranteed to be the closest
-    one to the target point. Thus, there is no need to scan all nodes.
-    Once the required k entries are extracted from the queue,
-    search can stop.
+    one to the target point among the remaining entries. Thus, there is no
+    need to scan all nodes. Once the required k entries are extracted from
+    the queue, search can stop.
   </para>
   </listitem>
 

doc/src/sgml/spgist.sgml

@@ -303,8 +303,8 @@
  </note>
 
  <para>
-  An index operator class for <acronym>SP-GiST</acronym> must provide one
-  optional and five mandatory user-defined methods. All five mandatory
+  An index operator class for <acronym>SP-GiST</acronym> must provide
+  five mandatory user-defined methods and can provide one optional method. All five mandatory
   methods follow the convention of accepting two <type>internal</> arguments,
   the first of which is a pointer to a C struct containing input values for
   the support method, while the second argument is a pointer to a C struct