diff --git a/asdf.texinfo b/asdf.texinfo
index cfef5c6..0d26235 100644
--- a/asdf.texinfo
+++ b/asdf.texinfo
@@ -338,6 +338,7 @@ option := :components component-list
 	| :output-files  method-form
         | :operation-done-p method-form
         | :depends-on ( {dependency-def}* ) 
+        | :weakly-depends-on ( {dependency-def}* ) 
 	| :serial [ t | nil ]
         | :in-order-to ( {dependency}+ )
 
@@ -381,6 +382,30 @@ is equivalent to
 	     (:file "c" :depends-on ("a" "b")))
 @end lisp
 
+@subsection Weakly-depends-on
+
+The @code{weakly-depends-on} argument says of the component depended on
+``if this component can be found, then impose a dependency, otherwise
+ignore it.''  At the top level, this can be useful for allowing a system
+to take advantage of another system, if it is present.  For example, a
+system might generate on-line documentation if a documentation
+generation system (like TINAA, Albert, etc.) was present.  A system that
+does text matching might do only simple matching but weakly depend on a
+regular expression system and, if that system is installed, would be
+able to also do regular expression matching.
+
+Notes:
+@itemize
+@item 
+It's not entirely clear to me that this option is very helpful at a
+level below the top-level.  Since it uses find-component, the behavior
+differs between top level and lower level; perhaps that needs to be
+explained.
+@item
+Presumably this will be most useful when complemented by some
+conditional loading construct in the system that has the dependency.
+What is that construct?
+@end itemize
 
 @subsection Source location
 
