diff --git a/src/apply/ref.xsl b/src/apply/ref.xsl
index bb94d73..c1a7be4 100644
--- a/src/apply/ref.xsl
+++ b/src/apply/ref.xsl
@@ -174,6 +174,10 @@
   increasing the argument count of @var{fnref} will @emph{decrease}
   the arity of the resulting reference and vice versa.
 
+  @emph{No validations are performed on arity}—if there exist more
+  arguments than the number of target function parameters, no error
+  will be raised.
+
   @var{fnref} must be a valid dynamic function reference.
 -->
 <function name="f:set-args" as="item()+">
@@ -202,4 +206,32 @@
   <sequence select="$args" />
 </function>
 
+
+<!--
+  Pushes @var{args} onto the argument list of @var{fnref}
+
+  This operates just as @code{f:set-args}, but retains existing arguments.
+-->
+<function name="f:push-args" as="item()+">
+  <param name="fnref" as="item()+" />
+  <param name="args"  as="item()*" />
+
+  <sequence select="f:set-args($fnref,
+                               (f:args( $fnref ), $args) )" />
+</function>
+
+
+<!--
+  Unshifts @var{args} onto the argument list of @var{fnref}
+
+  This operates just as @code{f:set-args}, but retains existing arguments.
+-->
+<function name="f:unshift-args" as="item()+">
+  <param name="fnref" as="item()+" />
+  <param name="args"  as="item()*" />
+
+  <sequence select="f:set-args($fnref,
+                               ($args, f:args( $fnref )) )" />
+</function>
+
 </stylesheet>
diff --git a/test/apply/ref.xspec b/test/apply/ref.xspec
index c3e67b1..86d0b2a 100644
--- a/test/apply/ref.xspec
+++ b/test/apply/ref.xspec
@@ -43,6 +43,7 @@
       <foo:a />
       <foo:b />
       <foo:c />
+      <foo:d />
     </foo:args>
   </variable>
 
@@ -396,4 +397,154 @@
               test="count( $x:result ) = 2" />
     </scenario>
   </scenario>
+
+
+  <scenario label="f:push-args mutator">
+    <scenario label="pushing arguments onto empty reference list">
+      <call function="f:push-args">
+        <param name="fnref"
+               select="$test-fn" />
+        <param name="args"
+               select="$args/foo:a,
+                       $args/foo:b" />
+      </call>
+
+      <expect label="retains target QName"
+              test="f:QName( $x:result ) = f:QName( $test-fn )" />
+
+      <expect label="reduces arity by number of arguments, relative to
+                     target function"
+              test="f:arity( $x:result ) = f:arity( $test-fn ) - 2" />
+
+      <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" />
+    </scenario>
+
+
+    <scenario label="pushing arguments onto populated reference
+                     list">
+      <call function="f:push-args">
+        <param name="fnref"
+               select="f:set-args( $test-fn,
+                                   ($args/foo:a,
+                                    $args/foo:b) )" />
+        <param name="args"
+               select="$args/foo:c,
+                       $args/foo:d" />
+      </call>
+
+      <expect label="retains target QName"
+              test="f:QName( $x:result ) = f:QName( $test-fn )" />
+
+      <expect label="reduces arity by number of arguments, relative to
+                     previous arity"
+              test="f:arity( $x:result ) = f:arity( $test-fn ) - 4" />
+
+      <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="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" />
+    </scenario>
+
+
+    <scenario label="pushing empty argument list onto populated
+                     reference list">
+      <call function="f:push-args">
+        <param name="fnref"
+               select="f:set-args( $test-fn,
+                                   ($args/foo:a,
+                                    $args/foo:b) )" />
+        <param name="args" select="()" />
+      </call>
+
+      <expect label="retains target QName"
+              test="f:QName( $x:result ) = f:QName( $test-fn )" />
+
+      <expect label="retains previous reference arity"
+              test="f:arity( $x:result ) = f:arity( $test-fn ) - 2" />
+
+      <expect label="retains previous arguments by reference"
+              test="f:args( $x:result )[ 1 ] is $args/foo:a
+                    and f:args( $x:result )[ 2 ] is $args/foo:b" />
+    </scenario>
+  </scenario>
+
+
+  <scenario label="f:unshift-args mutator">
+    <scenario label="unshifting arguments onto empty reference list">
+      <call function="f:unshift-args">
+        <param name="fnref"
+               select="$test-fn" />
+        <param name="args"
+               select="$args/foo:a,
+                       $args/foo:b" />
+      </call>
+
+      <expect label="retains target QName"
+              test="f:QName( $x:result ) = f:QName( $test-fn )" />
+
+      <expect label="reduces arity by number of arguments, relative to
+                     target function"
+              test="f:arity( $x:result ) = f:arity( $test-fn ) - 2" />
+
+      <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" />
+    </scenario>
+
+
+    <scenario label="unshifting arguments onto populated reference
+                     list">
+      <call function="f:unshift-args">
+        <param name="fnref"
+               select="f:set-args( $test-fn,
+                                   ($args/foo:a,
+                                    $args/foo:b) )" />
+        <param name="args"
+               select="$args/foo:c,
+                       $args/foo:d" />
+      </call>
+
+      <expect label="retains target QName"
+              test="f:QName( $x:result ) = f:QName( $test-fn )" />
+
+      <expect label="reduces arity by number of arguments, relative to
+                     previous arity"
+              test="f:arity( $x:result ) = f:arity( $test-fn ) - 4" />
+
+      <expect label="retains previous arguments by reference"
+              test="f:args( $x:result )[ 3 ] is $args/foo:a
+                    and f:args( $x:result )[ 4 ] is $args/foo:b" />
+
+      <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" />
+    </scenario>
+
+
+    <scenario label="unshifting empty argument list onto populated
+                     reference list">
+      <call function="f:unshift-args">
+        <param name="fnref"
+               select="f:set-args( $test-fn,
+                                   ($args/foo:a,
+                                    $args/foo:b) )" />
+        <param name="args" select="()" />
+      </call>
+
+      <expect label="retains target QName"
+              test="f:QName( $x:result ) = f:QName( $test-fn )" />
+
+      <expect label="retains previous reference arity"
+              test="f:arity( $x:result ) = f:arity( $test-fn ) - 2" />
+
+      <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" />
+    </scenario>
+  </scenario>
 </description>