Is there inconsistency in how these are displayed?
Groups, Hide and Highlight (1,4 & 3 in the screenshot) indicate the current state.
The Show only / Show all (2) icon displays the future state i.e. when all are displayed the icon indicates one topic if consistent with the above it would show two. Should this be changed to make them all consistent?
If so, this leaves the issue of how to deal the + / - in blocks. Perhaps something like the inset in the screenshot could be used.
