{
  "name": "z",
  "type": "function",
  "groups": ["GeometryGroup"],
  "description": "Returns the z coordinate of a point geometry, or NULL if the geometry has no z value.",
  "arguments": [ {"arg":"geometry","description":"a point geometry"}],
  "examples": [ { "expression":"z( geom_from_wkt( 'POINTZ(2 5 7)' ) )", "returns":"7"}
  ]
}