Treats the first row as a header and draws a separator beneath it. The double frame draws that separator heavier. The markdown border always carries its delimiter row. Turning this off puts a blank row above it.
Right-aligns a column whose non-empty body cells are all numeric. The header label is not judged, so a numeric column under a text header still aligns. An explicit align for that column wins.
How an over-wide cell is handled once maxWidth is set. wrap word-wraps onto multiple lines, truncate cuts with a trailing ellipsis. A GFM cell holds one line. The markdown border truncates whatever this says.