There have been lengthy discussions over the years whether a "Close" command makes sense in a single document interface application, which I would like to summarize:
There are four things Sigil could possibly do when the current (and only) book is closed:
- Close the book, followed by closing the application. That is what the File->Quit command already does.
- Close the book, followed by creating a new blank book. That is what the File->New command already does.
- Close the book, followed by opening another existing book. That is what the File->Open command does.
- Close the book, and leave you with a gray window with nothing in it. There is no command that does this at the moment.
Now many people have stated that the last option makes no sense, since the other three options exist. But in order to choose one of the other three ways to close a book, you need to know what you want to do next. If you don't, you have to pick a random one, knowing that part of the action performed is unnecessary, and possibly distracting. This is suboptimal.
On the other hand, having a separate Close command leaves the application in a new state which currently doesn't exist: an running Sigil instance with no current document to be worked on. This not only requires some programming work (e.g. graying out commands), but also introduces new questions as to the programs general behaviour in such a state.
In the end, it's not an easy choice to make. There are trade-offs on both sides of the equation.