Expand advice for optional icons with hidden labels

BS3 commits: 52e4b87b5a2ac6543f9a901946bea84966681216
Split out/clarify ``<select>`` and ``multiple``

BS3 commits: c918127e68ac320830f960ac8ab804378588db5b
Callout for labelling of input groups

BS3 commits: eee275762ff962121576f5aca93e0dfc52679d51
Make main segmented button keyboard-focusable

BS3 commits: 285ec7049393792503b2127932e4bc6a967d58b6
Use aria-label for pagination prev/next

BS3 commits: 24bc10266425cbb401ce9d4b681060159162a8b2