Suppose I've logged on to some system and want to run LibreOffice. But - which VCL should I use? I don't know! How can I check? Determing which VCLs are installed and available is obviously OS-distribution-dependent, no way to do that uniformly, ourselves. What better tool to check this, then, if not LibreOffice? But other than trial-and-error with every potential VCL, it doesn't look like LO lets us do this. So, I would like to have a command-line option, e.g. `--list-vcls`, which would print the list of VCLs which are known to be available/usable.