Clipboard
What a copy covers: the rows, the columns, and the text of every cell where they cross.
Handed to DataTable's onCopy. Both rows and columns are in display order, so a caller writing CSV, XLSX, or anything else gets the grid exactly as the user sees it — sorted, paged, and with hidden columns already gone.
Supplying onCopy replaces the table's own clipboard write rather than running alongside it, so a handler that only logs or displays the selection leaves the clipboard untouched. Call copyToSystemClipboard from inside it to do both.
Properties
Cell text, row-major: cells[row][column] lines up with rows and columns. Text is what the cell shows — each column's value put through its format — so a copy carries the same money symbols and dates the user was looking at. A column that renders only through cellContent copies as empty; give it a value and it becomes sortable and copyable at once. The raw values are still within reach for a handler that wants them: columns carries every column's own value extractor, and rows the items to run it against.
The selected leaf columns, in display order.