--- a/doc/manual.tex	Sun Dec 26 15:52:56 2010 -0500
+++ b/doc/manual.tex	Sun Dec 26 17:29:03 2010 -0500
@@ -2084,6 +2084,8 @@
 
 Normal links are accessible via HTTP \texttt{GET}, which the relevant standard says should never cause side effects.  To export a page which may cause side effects, accessible only via HTTP \texttt{POST}, include one argument of the page handler of type $\mt{Basis.postBody}$.  When the handler is called, this argument will receive a value that can be deconstructed into a MIME type (with $\mt{Basis.postType}$) and payload (with $\mt{Basis.postData}$).  This kind of handler will only work with \texttt{POST} payloads of MIME types besides those associated with HTML forms; for these, use Ur/Web's built-in support, as described below.
 
+Any normal page handler may also include arguments of type $\mt{option \; Basis.queryString}$, which will be handled specially.  Rather than being deserialized from the current URI, such an argument is passed the whole query string that the handler received.  The string may be analyzed by calling $\mt{Basis.show}$ on it.  A handler of this kind may be passed as an argument to $\mt{Basis.effectfulUrl}$ to generate a URL to a page that may be used as a ``callback'' by an external service, such that the handler is allowed to cause side effects.
+
 When the standalone web server receives a request for a known page, it calls the function for that page, ``running'' the resulting transaction to produce the page to return to the client.  Pages link to other pages with the \texttt{link} attribute of the \texttt{a} HTML tag.  A link has type $\mt{transaction} \; \mt{page}$, and the semantics of a link are that this transaction should be run to compute the result page, when the link is followed.  Link targets are assigned URL names in the same way as top-level entry points.
 
 HTML forms are handled in a similar way.  The $\mt{action}$ attribute of a $\mt{submit}$ form tag takes a value of type $\$\mt{use} \to \mt{transaction} \; \mt{page}$, where $\mt{use}$ is a kind-$\{\mt{Type}\}$ record of the form fields used by this action handler.  Action handlers are assigned URL patterns in the same way as above.