+=head3 RECURRING BILLING FIELDS
+
+=over 4
+
+=item interval
+
+Interval expresses the amount of time between billings: digits, whitespace
+and units (currently "days" or "months" in either singular or plural form).
+
+=item start
+
+The date of the first transaction (used for processors which allow delayed
+start) expressed as YYYY-MM-DD.
+
+=item periods
+
+The number of cycles of interval length for which billing should occur
+(inclusive of 'trial periods' if the processor supports recurring billing
+at more than one rate)
+
+=back
+
+=head2 test_transaction()
+
+Most processors provide a test mode, where submitted transactions will
+not actually be charged or added to your batch, calling this function
+with a true argument will turn that mode on if the processor supports
+it, or generate a fatal error if the processor does not support a test
+mode (which is probably better than accidentally making real charges).
+
+=head2 require_avs()
+
+Providing a true argument to this module will turn on address
+verification (if the processor supports it).
+
+=head1 TRANSACTION SUBMISSION METHOD
+
+=head2 submit()