diff --git a/src/apply/ref.xsl b/src/apply/ref.xsl
index c1a7be4..32b92ff 100644
--- a/src/apply/ref.xsl
+++ b/src/apply/ref.xsl
@@ -66,7 +66,7 @@
   <variable name="ns"
             select="namespace-uri-from-QName( $name )" />
 
-  <f:ref arity="{$arity}">
+  <f:ref arity="{$arity}" length="1">
     <element name="{$name}"
              namespace="{$ns}" />
   </f:ref>
@@ -200,6 +200,9 @@
     <attribute name="arity"
                select="$target-arity - count( $args )" />
 
+    <attribute name="length"
+               select="count( $args ) + 1" />
+
     <sequence select="$desc/*" />
   </f:ref>
 
@@ -234,4 +237,28 @@
                                ($args, f:args( $fnref )) )" />
 </function>
 
+
+<!--
+  Retrieve length of @var{fnref} as a number of sequence items
+
+  While the reference is intended to be opaque, it is no secret that
+  the data are stored as a sequence.  The length is therefore
+  important for stepping through that sequence of data, similar to how
+  data/struct length are required for pointer arithmetic when dealing
+  with memory in C.
+
+  So, this doesn't break encapsulation: it just tells us how big we
+  are, which is an external quality that can be easily discovered
+  without our help; we just cache it for both performance and
+  convenience.  Aren't we nice?
+-->
+<function name="f:length" as="xs:double">
+  <param name="fnref" as="item()+" />
+
+  <variable name="desc" as="element( f:ref )"
+            select="$fnref[ 1 ]" />
+
+  <sequence select="number( $desc/@length )" />
+</function>
+
 </stylesheet>
diff --git a/test/apply/ref.xspec b/test/apply/ref.xspec
index 86d0b2a..cc67ffe 100644
--- a/test/apply/ref.xspec
+++ b/test/apply/ref.xspec
@@ -68,6 +68,13 @@
 
       <expect label="produces reference to expected QName"
               test="f:QName( $x:result ) = $qname" />
+
+      <!-- this isn't breaking encapsulation: we know that a sequence
+           is returned and we must know how to delimit the references
+           within it -->
+      <expect label="produces length equal to length of returned
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
 
 
@@ -281,6 +288,10 @@
 
       <expect label="retains target arity"
               test="f:arity( $x:result ) = f:arity( $test-fn )" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
 
 
@@ -296,6 +307,10 @@
       <!-- the function is now partially applied -->
       <expect label="reduces arity by number of arguments"
               test="f:arity( $x:result ) = f:arity( $test-fn ) - 2" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
 
 
@@ -313,6 +328,10 @@
       <!-- the function is no longer partially applied -->
       <expect label="restores target function arity"
               test="f:arity( $x:result ) = f:arity( $test-fn )" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
 
 
@@ -330,6 +349,10 @@
       <!-- the function is no longer partially applied -->
       <expect label="reduces arity by number of argments"
               test="f:arity( $x:result ) = f:arity( $test-fn ) - 3" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
 
 
@@ -347,6 +370,10 @@
       <!-- the function is no longer partially applied -->
       <expect label="increases arity by difference in argument count"
               test="f:arity( $x:result ) = f:arity( $test-fn ) - 1" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
   </scenario>
 
@@ -419,6 +446,10 @@
       <expect label="sets arguments by reference"
               test="f:args( $x:result )[ 1 ] is $args/foo:a
                     and f:args( $x:result )[ 2 ] is $args/foo:b" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
 
 
@@ -448,6 +479,10 @@
       <expect label="pushes new arguments by reference"
               test="f:args( $x:result )[ 3 ] is $args/foo:c
                     and f:args( $x:result )[ 4 ] is $args/foo:d" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
 
 
@@ -470,6 +505,10 @@
       <expect label="retains previous arguments by reference"
               test="f:args( $x:result )[ 1 ] is $args/foo:a
                     and f:args( $x:result )[ 2 ] is $args/foo:b" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
   </scenario>
 
@@ -494,6 +533,10 @@
       <expect label="sets arguments by reference"
               test="f:args( $x:result )[ 1 ] is $args/foo:a
                     and f:args( $x:result )[ 2 ] is $args/foo:b" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
 
 
@@ -523,6 +566,10 @@
       <expect label="unshifts new arguments by reference"
               test="f:args( $x:result )[ 1 ] is $args/foo:c
                     and f:args( $x:result )[ 2 ] is $args/foo:d" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
 
 
@@ -545,6 +592,10 @@
       <expect label="retains previous arguments by reference"
               test="f:args( $x:result )[ 1 ] is $args/foo:a
                     and f:args( $x:result )[ 2 ] is $args/foo:b" />
+
+      <expect label="produces length equal to length of constructed
+                     sequence"
+              test="f:length( $x:result ) = count( $x:result )" />
     </scenario>
   </scenario>
 </description>