Content type versioning
All changes to a content type are recorded in a version history. The version number will reflect the workflow state that the content type is in. When a content type is first created its version number will be 0.1.
Saving a content type
Each time a change is made to a content type and saved, the minor version number is incremented and the changes are recorded in a version history.
For example, adding a field to a newly created content type and pressing Save would increment the version number from 0.1 to 0.2.
Publishing a content type
When a content type is ready for publishing, pressing Publish in the Content type builder will change the major version number.
For example, having added all my fields to a newly created content type and saved it, pressing Publish increments the version number from 0.2 to 1.0 and changes the workflow state of the content type to Published.