An Extensible Template may be extended in an Application generating SOP Instances to include additional Content Items in its definition. Such Content Items shall not duplicate concepts for which an encoding is defined in the Template. I.e., if a method is provided for the encoding of a concept in the Template, that concept shall not be encoded using a different Content Item in an extension to the Template.
Note: There is no requirement that the included additional Content Items in a Template extension be placed at the end of the Template. The additional Content Items may be included at any semantically appropriate location in the Template, regardless of whether the order of Content Items in the Template is significant.
A Non-extensible Template shall not be modified in an Application by the addition of Content Items to its definition.
Notes: The set of Content Items in either an Extensible or a Non-extensible Template may be changed in subsequent editions of the Standard, in accordance with the procedures of the DICOM Standards Committee.
A Non-Extensible Template may include a Template that is Extensible. In invoking such a Template, the content structure of SOP Instances created from the Non-Extensible Template may vary according to the varying content structure allowed by the extension of the included Template.
Note: Specification of such extensible content in a Non-Extensible Template may be desirable if the Template defines, e.g., a fixed top level structure into which a variety of lower level structures may be "plugged".