Each message described in this section is an XML message conforming to the XML Schema in Appendix: Message XML Schema. A list of the fields used and the format can be found in 'Appendix: Data dictionary'.  The IDs used in the messages are explained in 'Appendix: IDs' in the 'iDEAL_010 Standards' document.

In the message overviews, indicated fields are mandatory unless otherwise is indicated (as followed):

• Optional: The element may optinally occur and if so must occur exactly once.
• Conditional: The lement occurs once depending on the situation.
• (1..∞): The element must occur one or more (unlimited) times.

The message tables include the parent elements in bold, which contain sub-elements. Some sub-elements are also parent elements.

HTTP

The following HTTP header must be used for all messages:

• All messages must comply with the HTTP 1.1 standard. 
• Each XML request message must be sent as the body of an HTTP POST message.
• Each XML response message must be sent as the body of an HTTP 200 OK message.

XML header

The following XML header must be used for all messages:

Character set

• In all iDEAL messages the Unicode character set must be used. Only the MES-2 subset must be supported.
• Encoding must be used as indicated in the HTTP and XML headers UTF-8 (Unicode Transformation Format). 
• The Byte Order Mark (BOM) must not be used. The UTF-8 representation of the BOM is the byte sequence 0xEF,0xBB,0xBFs.

Conventions for empty fields

In iDEAL an XML tag for an optional or conditional field is either:

• present (in which case, the tag must be filled with a valid value)
• or not present at all.

Message validation

All messages must be validated against the iDEAL XML Schema. The schema also references the XML Digital Signature Schema which must be used to validate the Signature element. The XML Digital Signature Schema is available from W3C at the following URL: http://www.w3.org/2000/09/xmldsig#. If additional validation of specific fields is required, it is indicated in the field specification.

Message version

The namespace of all messages described in this document holds the version of the messages. 
For backward compatibility all XML message content (requests and [error] responses) must contain a version attribute in the root element, as shown in the table below.