+=item C<get_taxkey %params>
+
+Retrieves and returns a taxkey object valid for the given date
+C<$params{date}> and tax zone C<$params{taxzone}>
+(C<$params{taxzone_id}> is also recognized). The date defaults to the
+current date if undefined.
+
+This function looks up the income (for trueish values of
+C<$params{is_sales}>) or expense (for falsish values of
+C<$params{is_sales}>) account for the current part. It uses the part's
+associated buchungsgruppe and uses the fields belonging to the tax
+zone given by C<$params{taxzone}> (range 0..3).
+
+The information retrieved by the function is cached.
+
+=item C<get_chart %params>
+
+Retrieves and returns a chart object valid for the given type
+C<$params{type}> and tax zone C<$params{taxzone}>
+(C<$params{taxzone_id}> is also recognized). The type must be one of
+the three key words C<income>, C<expense> and C<inventory>.
+
+This function uses the part's associated buchungsgruppe and uses the
+fields belonging to the tax zone given by C<$params{taxzone}> (range
+0..3).
+
+The information retrieved by the function is cached.
+
+=item C<orphaned>
+
+Checks if this articke is used in orders, invoices, delivery orders or
+assemblies.
+
+=item C<buchungsgruppe BUCHUNGSGRUPPE>