module _3gpp-common-yang-extensions {
  yang-version 1.1;
  namespace urn:3gpp:sa5:_3gpp-common-yang-extensions ;
  prefix yext3gpp ;

  organization "3GPP SA5";
  description "The module defines YANG extensions needed 
    3GPP YANG modeling.

    Copyright (c) 2019 3GPP. All rights reserved.

    Extensions MUST be defined with the following structure in the
    description statement:
        - What is this statement.
        - Newline,
        - This statement can be a substatement of the xxx statements with
        cardinality x..y.
        - This statement can have the following substatements with
        cardinality x..y.
        - Newline
        - Is changing this statement an editorial, BC(backwards compatible) 
        or NBC(non-BC) change?
        - Newline.
        - The argument its meaning and type. Preferably use YANG types and
          constraints to define the argument's type.

    Any extension statement can be added with a
    deviation/deviate add statement. In this case the restriction about
    the parent statement of the extension SHALL be evaluated based on the
    target of the deviation statement.

    Support for this module does not mean that a YANG server implements
    support for each of these extensions.
    Implementers of each specific module using an extensions MUST check
    if the server implements support for the used extension.
    Note: modules use many extensions which individual
    implementations MAY or MAY NOT support.
    If support for an extension is missing the extension statement needs
    individual handling or it SHOULD be removed from the module using
    the extension e.g. with a deviation.
          ";

  revision "2019-06-23" {
    description "Initial version";
  }

  extension inVariant {
    description
      "Indicates that the value for the data node can only be set when its
      parent data node is being created. To change the value after that, the
      parent data node must be deleted and recreated with the data node
      having the new value.

      It is unnecessary to use and MUST NOT be used for key leafs.

      The statement MUST only be a substatement of a leaf, leaf-list, list 
      statements that is config=true.
      Zero or one inVariant statement is allowed per parent statement.
      NO substatements are allowed.
            
      Adding this statement is an NBC change, removing it is BC.";
  }

  extension initial-value {
    description "Specifies a value that the system will set for a leaf
      leaf-list if a value is not specified for it when its parent list
      or container is created. The value has no effect in any other
      modification e.g. changing or removing the value.

      The description statement of the parent statement SHOULD contain
      the label 'Initial-value: ' followed by the text from the argument.

      The statement MUST only be a substatement of a leaf or leaf-list.
      The statement MUST NOT be present if the leaf or the leaf-list 
      has a default statement or the type used for the data node 
      has a default value.
      The statement MUST NOT be used for config=false data or in an 
      action, rpc or notification.
      Zero or one initial-value statements are allowed for a leaf parent
      statement. Zero or more initial-value statements are allowed for a
      leaf-list parent statement. If the leaf-list is ordered-by user, the
      initial values are stored in the order they appear in the YANG definition.
      NO substatements are allowed.

      Always consider using a YANG-default statement instead.

      Modification of the initial-value is a non-backwards-compatible change.

      The argument specifies a single initial value for a leaf or leaf-list.
      The value MUST be part of the valuespace of the leaf/leaf-list.
      It follows the same rules as the argument of the default statement.";

    argument "initial-value";
  }
}