Im looking at how to create an RFQ  but i cant see some fields in the purchase.order model, 

in the browser the user can add products to the RFQ and their properties such as:

Description, Scheduled Date, Quantity , Unit Price, Product, 

However, the  Taxes field seems to be present. 

there is nothing akin these fields in the model:

models.execute_kw(
 db, uid, password, 'purchase.order', 'fields_get',
 [], {'attributes': ['string', 'help', 'type']})

i only see these fields:

['__last_update', 'amount_tax', 'amount_total', 'amount_untaxed', 'bid_date', 'bid_validity', 'company_id', 'create_date', 'create_uid', 'currency_id', 'date_approve', 'date_order', 'dest_address_id', 'display_name', 'fiscal_position', 'id', 'incoterm_id', 'invoice_count', 'invoice_ids', 'invoice_method', 'invoiced', 'invoiced_rate', 'journal_id', 'location_id', 'message_follower_ids', 'message_ids', 'message_is_follower', 'message_last_post', 'message_summary', 'message_unread', 'minimum_planned_date', 'name', 'notes', 'order_line', 'origin', 'partner_id', 'partner_ref', 'payment_term_id', 'picking_ids', 'picking_type_id', 'pricelist_id', 'product_id', 'related_location_id', 'related_usage', 'requisition_id', 'shipment_count', 'shipped', 'shipped_rate', 'state', 'validator', 'write_date', 'write_uid']