Polished tuff stairs

Since 1.21

Bottom slab + upper step filling the north-west, north-east quarter(s)

One step lighter

The next band up in a gradient: same hue, no hard line.

One step darker

The next band down: shade under ledges and at the base.

Frame

A log or polished stone that contrasts in value, one block in front of the fill.

Accent

A colour for about a tenth of the build, at the focal point.

80 combinations

facing north, south, west, east: Side of the tall back. The full-height step occupies the half of the cell on the facing side; a player walking in the facing direction climbs the stair. The low tread (open side) faces the opposite way. Example facing=north: tall part in z 0..8 (north half), tread open to the south.
half top, bottom: bottom = normal stair (slab at the bottom, step on top). top = upside-down stair: the slab is the upper half and the step hangs below it, still on the facing side. Seen from the open side an upside-down stair is a corbel or cornice: full at the top, cut away underneath toward the open side.
shape straight, inner_left, inner_right, outer_left, outer_right: Corner form, normally computed from the neighbouring stairs (set it yourself in a paste). left and right are seen looking in the facing direction (standing on the tread, facing the back). inner = L-shaped step (three quarters tall), used on the concave corner of two stair runs. outer = a single tall quarter, used on the convex corner. Checked on the 26.2 outlines for facing=north: inner_left adds the south-west quarter, inner_right the south-east quarter, outer_left keeps only the north-west quarter, outer_right only the north-east quarter.
waterlogged true, false: true puts a water source inside the block (water renders around it). Always false for dry builds.