+=head2 C<CURRENT>
+
+The current level - i.e. C<0>.
+
+=head2 C<UP $from>
+
+The level of the scope just above C<$from>.
+
+=head2 C<DOWN $from>
+
+The level of the scope just below C<$from>.
+
+=head2 C<SUB $from>
+
+The level of the closest subroutine context above C<$from>.
+
+=head2 C<EVAL $from>
+
+The level of the closest eval context above C<$from>.
+
+If C<$from> is omitted in any of those functions, the current level is used as the reference level.
+