Add Expand All / Collapse All buttons to any matrix with hierarchy rows using bookmark-based visibility toggle.

Your matrix has two or three row levels — a user opens the report and sees everything collapsed. They click the expand arrow on each row, one by one, to see the detail. There's no "Expand All" button in Power BI. Building one yourself means duplicating the matrix with pinned expansion states, creating two action buttons with bookmark-based visibility toggle, writing bookmark files that correctly show/hide four visuals at once, and getting the VCO formatting right so the buttons don't look broken. This skill builds the entire toggle — expanded matrix, buttons, bookmarks, and visibility wiring — in one command.