top_up.rb
 1form!
 2title "Buy Account Credit"
 3
 4field(
 5	type: "fixed",
 6	label: "Current balance",
 7	value: "$#{'%.2f' % @balance}"
 8)
 9
10field(**@payment_methods.to_list_single)
11
12field(
13	datatype: "xs:decimal",
14	range: @range,
15	var: "amount",
16	label: "Amount of credit to buy",
17	prefix: "$",
18	required: true
19)