Adds a sort parameter, order have to be in ['ascend', 'ascending','descend', 'descending','custom']

def _addSortParam(self, field, order=''):
		"""Adds a sort parameter, order have to be in ['ascend', 'ascending','descend', 'descending','custom']"""

		if order != '':
			validSortOrders = {
				'ascend':'ascend',
				'ascending':'ascend',
				'<':'ascend',
				'descend':'descend',
				'descending':'descend',
				'>':'descend'
			}

			if not string.lower(order) in validSortOrders.keys():
				raise FMError, 'Invalid sort order for "' + field + '"'

		self._sortParams.append(
			[field, validSortOrders[string.lower(order)]]
		)