diff --git a/handbook/porting.sgml b/handbook/porting.sgml
index 0d3b5bcc75..16af9d3da8 100644
--- a/handbook/porting.sgml
+++ b/handbook/porting.sgml
@@ -1,4 +1,4 @@
-<!-- $Id: porting.sgml,v 1.111 1998-10-05 15:10:42 motoyuki Exp $ -->
+<!-- $Id: porting.sgml,v 1.112 1998-10-09 10:50:56 asami Exp $ -->
 <!-- The FreeBSD Documentation Project -->
 
 <sect1><heading>Porting an existing piece of free software<label id="porting"></heading>
@@ -946,6 +946,11 @@ FETCH_DEPENDS=   ncftp2:${PORTSDIR}/net/ncftp2
 	      unsupported.  (I.e., it may still work if you know what
 	      you are doing, but you are on your own.)
 
+	    <p>Note: if a port only works for a.out, set
+	      <tt/BROKEN_ELF/ to a string describing the reason why.
+	      Such ports will be skipped during a build on an ELF
+	      system.
+
 	  <sect3>
 	    <heading>PORTOBJFORMAT</heading>
 
@@ -1019,6 +1024,14 @@ PORTOBJFORMAT!= test -x /usr/bin/objformat && /usr/bin/objformat || echo aout
 	      minor number from long shlib names if <tt/PORTOBJFORMAT/
 	      equals <tt/elf/.
 
+	    <p>In cases where you really need to install shlibs with
+	      two versions on an ELF system or those with one version
+	      on an a.out system (for instance, ports that install
+	      compatibility libraries for other operating systems),
+	      define the variable <tt/NO_FILTER_SHLIBS/.  This will
+	      turn off the editing of <tt/PLIST/ mentioned in the
+	      previous paragraph.
+
 	  <sect3>
 	    <heading><tt/ldconfig/</heading>