An empty box- NONE of the SELECTED images have this keyword.
A dash in the box- SOME of the SELECTED images have this keyword.
A tick in the box- ALL of the SELECTED images have this keyword.
Mouse click in an empty box- adds that keyword to selected images.
Mouse click in an ticked box- deletes that keyword from the selected images.
Click the arrow next to the number of images with a keyword, will filter the grid to show only those images-
Please can you confirm if it's possible to use keyword shortcuts with more than one keyword at a time? That is, can you add more than one + sign to add multiple keywords at a time?
Not sure what you mean by 'keyword shortcuts'
You can only define one keyword by clicking on the + in the [Keyword List] header. This just adds a new keyword to the list (and selected photos if option is set)
If you set the menu beside Keyword tags: to [Enter Keywords]-
You can select any (one or more) photo/s and type multiple keywords in the large text window, each keyword separated by a comma. Then press [Enter]- all the keywords are added to the list and the selected photo/s.
It is possible to select (high-light) all the keywords visible in this window (drag the mouse) and do a copy [Ctrl+c], select multiple photos in the grid and paste all the keywords [Ctrl+v] to other selected photos. This way you can add many of the same keywords to many photos with simple copy&paste.