This is a virtual special issue (VSI), which means that submitted papers will be handled as part of the normal submission flow of the journal, but will be designated as belonging to the special issue. Accepted articles will be published in the first available regular issue and will simultaneously appear in a special section dedicated to VSIs. In this way, the content of the special issue can be called up at any time and it will be continuously expanding. A VSI is not published in one batch, but emerges over time as each contribution is published when ready. The implication of this VSI format is that it operates on an open deadline, making the publication process dynamic and timely.