The following conventions are used to indicate whether a message element is mandatory:

Yes: The element must occur exactly once.
No: The element may not occur, or it must occur exactly once.
Yes (1..∞): The element must occur one or more (unlimited) times.

HTTP

The following HTTP header must be used for all messages:

Data element	Mandatory	Explanation
`content-type`	Yes	Defines how the remainder of the content is to be interpreted. Contains the value: `text/xml; charset="utf-8"`.

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:

<?xml version="1.0" encoding="UTF-8"?>

Character set

In all 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

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 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.

Attribute	Mandatory	Explanation
`version`	Yes	Value must be: `3.3.1`

Message validation

All messages must be validated against the provided 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.

Browser not supported