Almost all ISO standards contain at present a so-called "conformance clause". There are enumerated the requirements a product has to satisfy in order to permit to call it conforming to ISO xxx. Standards for coded character sets include similar regulations. Although testing of products in this field is out of the scope of this handbook, it may be instructive to elucidate the concepts ISO is applying in the respective standards.
The following is taken literally from ISO 4873:1991, in the other coding standards an almost identical text is included.
4.6. coded-character-data-element (CC-data-element): An element of interchanged information that is specified to consist of a sequence of coded representations of characters, in accordance with one or more identified standards for coded character sets.
4.12. device: A component of information processing equipment which can transmit, and/or receive, coded information with CC-data-elements.
4.18. user: A person or other entity that invokes the services provided by a device.
2. Conformance and implementation
2.1.1. Conformance of information interchange
A coded-character-data-element (CC-data-element) within coded information for interchange is in conformance with a version of this International Standard if all the coded representations of characters within that CC-data-element conform to the requirements of clause 9. A claim of conformance shall identify the version adopted.
2.1.2. Conformance of devices
A device is in conformance with this International Standard if it conforms to the requirements of 18.104.22.168, and either or both of 22.214.171.124 and 126.96.36.199. A claim of conformance shall identify the document which contains the description specified in 188.8.131.52, and shall identify the version adopted.
184.108.40.206. Device description
A device that conforms to this International Standard shall be the subject of a description that identifies the means by which the user may supply characters to the device, or may recognize them when they are made available to him, as specified respectively in 220.127.116.11 and 18.104.22.168.
22.214.171.124. Originating devices
An originating device shall allow its user to supply any sequence of characters from the version adopted, and shall be capable of transmitting their coded representations within a CC-data-element.
126.96.36.199. Receiving devices
A receiving device shall be capable of receiving and interpreting any coded representations of characters that are within a CC-data-element, and that conform to 2.1.1, and shall make the corresponding characters available to its user in such a way that the user can identify them from among those of the version adopted, and can distinguish them from each other.
The use of this code requires definitions of its implementation in various media. For example, these could include punched tapes, punched cards, magnetic and optical media and transmission channels, thus permitting interchange of data to take place either indirectly by means of an intermediate recording in a physical medium, or by local connection of various units (such as input and output devices and computers) or by means of data transmission equipment.
The implementation of this code in physical media and for transmission, taking into account the need for error checking, is the subject of other International Standards.