Doc: minor cleanups.

Improve a couple of things I noticed while working on v15
release notes.

doc/src/sgml/config.sgml

@@ -10838,9 +10838,10 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
      will accept a setting for any two-part parameter name.  Such variables
      are treated as placeholders and have no function until the module that
      defines them is loaded. When an extension module is loaded, it will add
-     its variable definitions, convert any placeholder values according to
+     its variable definitions and convert any placeholder values according to
-     those definitions, and issue warnings for any unrecognized placeholders
+     those definitions.  If there are any unrecognized placeholders
-     that begin with its extension name.
+     that begin with its extension name, warnings are issued and those
+     placeholders are removed.
     </para>
    </sect1>
 

doc/src/sgml/ref/pgupgrade.sgml

@@ -768,11 +768,13 @@ psql --username=postgres --file=script.sql postgres
 
   <para>
    <application>pg_upgrade</application> creates various working files, such
-   as schema dumps, stored within <literal>pg_upgrade_output.d</literal> in
+   as schema dumps, stored within <filename>pg_upgrade_output.d</filename> in
    the directory of the new cluster. Each run creates a new subdirectory named
    with a timestamp formatted as per ISO 8601
-   (<literal>%Y%m%dT%H%M%S</literal>), where all the generated files are
+   (<literal>%Y%m%dT%H%M%S</literal>), where all its generated files are
    stored.
+   <filename>pg_upgrade_output.d</filename> and all its contained files may be
+   removed once the upgrade is successfully completed.
   </para>
 
   <para>