meaningof the segment Version in field description jira API

[Abdullah Sa'D Muhammad Answar Vencapah]

{"fields":{    "description": {

            "version": 1, the meaning of the version in jira api

            "type": "doc",

            "content": [

                {

                    "type": "paragraph",

                    "content": [

                        {

                            "type": "text",

                            "text": "my new test"

                        }

                    ]

                }

            ]

        }

How I can merge a new value in field description with the old one?
For example old value + new value need to be the result when merging in jira api 

[Nic Brough -Adaptavist-]

It means the issue has a version set (versions are a project-specfic drop-down list, with the contents being set by the project admins)