One cell of the tool cluster: the tool it arms, the group it sits in, and
what the status line says while it is armed. Its face is an icon alone;
the tooltip carries the words.
Which part of the tool cluster a cell sits in. A cluster rules a line
between neighbours of different groups, so every shell draws the same
boundaries.
The cluster’s cells, in the order it lays them out — most used first,
which is the order the digit shortcuts run in. One list: membership,
order, grouping, and the line the status line reads while each is armed.
The toolbar button that should show as selected while active is the current
tool. A base toolbar tool maps to itself; a sub-tool maps to the base tool it
originates from so exactly one toolbar button is always highlighted. Route
editing sub-tools are selection operations, so they (like every selection
microtool and any other non-toolbar tool) map to Select as the safe default.
The result is always a member of BAND_TOOLS.