{
  "name": "overlay_within",
  "type": "function",
  "groups": ["GeometryGroup"],
  "description": "Returns whether the current feature is spatially within at least one feature from a target layer, or an array of expression-based results for the features in the target layer that contain the current feature.<br><br>Read more on the underlying GEOS \"Within\" predicate, as described in PostGIS <a href='https://postgis.net/docs/ST_Within.html'>ST_Within</a> function.",
  "arguments": [
    {
      "arg": "layer",
      "description": "the layer whose overlay is checked"
    },
    {
      "arg": "expression",
      "description": "an optional expression to evaluate on the features from the target layer. If not set, the function will just return a boolean indicating whether there is at least one match.",
      "optional": true
    },
    {
      "arg": "filter",
      "description": "an optional expression to filter the target features to check. If not set, all the features will be checked.",
      "optional": true
    },
    {
      "arg": "limit",
      "description": "an optional integer to limit the number of matching features. If not set, all the matching features will be returned.",
      "optional": true
    },
    {
      "arg": "cache",
      "description": "set this to true to build a local spatial index (most of the time, this is unwanted, unless you are working with a particularly slow data provider)",
      "optional": true,
      "default": "false"
    }
  ],
  "examples": [
    {
      "expression": "overlay_within('regions')",
      "returns": "true if the current feature is spatially within a region"
    },
    {
      "expression": "overlay_within('regions', filter:= population > 10000)",
      "returns": "true if the current feature is spatially within a region with a population greater than 10000"
    },
    {
      "expression": "overlay_within('regions', name)",
      "returns": "an array of names, for the regions containing the current feature"
    },
    {
      "expression": "array_to_string(overlay_within('regions', name))",
      "returns": "a string as a comma separated list of names, for the regions containing the current feature"
    },
    {
      "expression": "array_sort(overlay_within(layer:='regions', expression:=\"name\", filter:= population > 10000))",
      "returns": "an ordered array of names, for the regions containing the current feature and with a population greater than 10000"
    },
    {
      "expression": "overlay_within(layer:='regions', expression:= geom_to_wkt($geometry), limit:=2)",
      "returns": "an array of geometries (in WKT), for up to two regions containing the current feature"
    }
  ]
}