What complex interaction pattern does this implement?
const grid = document.querySelector('.grid');
let selection = new Set();
grid.addEventListener('click', e => {
const cell = e.target.closest('.cell');
if (!cell) return;
if (e.shiftKey && lastSelected) {
const cells = Array.from(grid.querySelectorAll('.cell'));
const start = cells.indexOf(lastSelected);
const end = cells.indexOf(cell);
const range = cells.slice(
Math.min(start, end),
Math.max(start, end) + 1
);
range.forEach(cell => selection.add(cell));
} else if (e.ctrlKey || e.metaKey) {
selection[selection.has(cell) ? 'delete' : 'add'](cell);
} else {
selection.clear();
selection.add(cell);
}
lastSelected = cell;
updateSelection();
});
This implements a sophisticated multi-select pattern with modifier key support through event delegation. Features include: 1) Single-click selection clearing previous selection, 2) Ctrl/Cmd-click for toggling individual cells, 3) Shift-click for range selection, 4) Efficient handling through delegation, 5) State management using Set, 6) Support for discontinuous selection. This pattern mirrors OS-style selection behavior while maintaining the benefits of event delegation.