I just added the following section to the author instructions to address submissions that are extended versions of conference/workshop papers:
We accept extended versions of works previously published at workshops or conferences under the following conditions:
The previous publication is clearly and prominently indicated and referenced
The additions and differences are described in the introduction
At least 25% of the content of the extended version are new
The extended version covers significant additional elements, and is not just a more verbose version of the previous content
It is furthermore the authors’ responsibility to ensure that the publication of the extended version complies with the requirements (including copyright) of the previous publisher.
I just added the following section to the author instructions to address submissions that are extended versions of conference/workshop papers:
Let us know if you have comments on this.