Add a section on working with readonly sysclt(8) oids. Use an example which

I've seen, both on my laptop and in mailing lists.

Fix some spelling errors.  These should be considered whitespace, and should
have been seperated.  However my content change was only in one place so
translators should see this easily.  Sorry in advance.

en_US.ISO8859-1/books/handbook/config/chapter.sgml

@@ -1215,6 +1215,41 @@ kern.maxfiles: 2088 -> 5000</screen>
     <para>Settings of sysctl variables are usually either strings,
       numbers, or booleans (a  boolean being <literal>1</literal> for yes
       or a <literal>0</literal> for no).</para>
+      
+  <sect2 id="sysctl-readonly">
+    <sect2info>
+      <authorgroup>
+        <author>
+	 <firstname>Tom</firstname>
+	 <surname>Rhodes</surname>
+	 <contrib>Contributed by </contrib>
+	 <!-- 31 January 2003 -->
+        </author>
+      </authorgroup>
+    </sect2info>
+    <title>&man.sysctl.8; read only</title>
+    
+    <para>In some cases it may be desirable to modify read-only &man.sysctl.8;
+      values.  While this is not recommended, it is also sometimes unavoidable.</para>
+      
+    <para>For instance on some laptop models the &man.cardbus.4; device will
+      not probe memory ranges, and fail with errors which look similar to:</para>
+      
+    <screen>cbb0: Could not map register memory</screen>
+    <screen>device_probe_and_attach: cbb0 attach returned 12</screen>
+    
+    <para>Cases like the one above usually require the modification of some
+      default &man.sysctl.8; settings which are set read only.  To overcome
+      these situations a user can put &man.sysctl.8; <quote>OIDs</quote>
+      in their local <filename>/boot/loader.conf.local</filename>.  Default
+      settings are located in the <filename>/boot/defaults/loader.conf</filename>
+      file.</para>
+      
+    <para>Fixing the problem mentioned above would require a user to set
+      <option>hw.pci.allow_unsupported_io_range=1</option> in the aforementioned
+      file.  Now &man.cardbus.4; will work properly.</para>
+    
+    </sect2>
   </sect1>
 
   <sect1 id="configtuning-disk">
@@ -1264,7 +1299,7 @@ kern.maxfiles: 2088 -> 5000</screen>
  	  typically occurs when writing large sequential files.  The idea
  	  is to avoid saturating the buffer cache with dirty buffers when
  	  it would not benefit I/O performance.  However, this may stall
- 	  processes and under certain cirucstances you may wish to turn it
+ 	  processes and under certain circumstances you may wish to turn it
  	  off.</para>
        </sect3>
  
@@ -1283,7 +1318,7 @@ kern.maxfiles: 2088 -> 5000</screen>
  	  Note that setting too high a value (exceeding the buffer cache's
  	  write threshold) can lead to extremely bad clustering
  	  performance.  Do not set this value arbitrarily high!  Higher
- 	  write values may add latency to reads occuring at the same time.
+ 	  write values may add latency to reads occurring at the same time.
  	</para>
  
  	<para>There are various other buffer-cache and VM page cache
@@ -1313,7 +1348,7 @@ kern.maxfiles: 2088 -> 5000</screen>
  	  you need it, because the tradeoff you are making is essentially
  	  pre-page memory sooner rather than later; thus eating more swap
  	  and disk bandwidth.  In a small system this option will have a
- 	  determinal effect but in a large system that is already doing
+ 	  determinable effect but in a large system that is already doing
  	  moderate paging this option allows the VM system to stage whole
  	  processes into and out of memory easily.</para>
        </sect3>
@@ -1392,7 +1427,7 @@ kern.maxfiles: 2088 -> 5000</screen>
 
       <para>Soft Updates drastically improves meta-data performance, mainly 
         file creation and deletion, through the use of a memory cache.  We
-        recommend to use Soft Updates on all of your filesystems.  There
+        recommend to use Soft Updates on all of your file systems.  There
         are two downsides to Soft Updates that you should be aware of:  First,
         Soft Updates guarantees filesystem consistency in the case of a crash
         but could very easily be several seconds (even a minute!) behind
@@ -1408,7 +1443,7 @@ kern.maxfiles: 2088 -> 5000</screen>
 	
 	<indexterm><primary>Soft Updates (Details)</primary></indexterm>
 
-	<para>There are two traditional approaches to writing a filesystems meta-data
+	<para>There are two traditional approaches to writing a file systems meta-data
     	  back to disk.  (Meta-data updates are updates to
 	  non-content data like inodes or directories.)</para>
 	
@@ -1517,11 +1552,11 @@ kern.maxfiles: 2088 -> 5000</screen>
 	   the <emphasis>background fsck</emphasis>: at system startup
 	   time, only a <emphasis>snapshot</emphasis> of the
 	   filesystem is recorded.  The <command>fsck</command> can be
-	   run later on.  All filesystems can then be mounted
+	   run later on.  All file systems can then be mounted
 	   <quote>dirty</quote>, so the system startup proceeds in
 	   multiuser mode.  Then, background <command>fsck</command>s
-	   will be scheduled for all filesystems where this is required, to free
-	   resources that may be unused.  (Filesystems that do not use
+	   will be scheduled for all file systems where this is required, to free
+	   resources that may be unused.  (File systems that do not use
 	   Soft Updates still need the usual foreground
 	   <command>fsck</command> though.)</para>