diff --git a/resources/function_help/json/$x b/resources/function_help/json/$x
index ceb8e9bc74c..13d0c24a483 100644
--- a/resources/function_help/json/$x
+++ b/resources/function_help/json/$x
@@ -2,7 +2,7 @@
   "name": "$x",
   "type": "function",
   "groups": ["GeometryGroup"],
-  "description": "Returns the x coordinate of the current feature.",
+  "description": "Returns the x coordinate of the current point feature.",
   "examples": [ { "expression":"$x", "returns":"42"}
   ]
 }
diff --git a/resources/function_help/json/$y b/resources/function_help/json/$y
index da9925e3d1b..51c373f15d3 100644
--- a/resources/function_help/json/$y
+++ b/resources/function_help/json/$y
@@ -2,7 +2,7 @@
   "name": "$y",
   "type": "function",
   "groups": ["GeometryGroup"],
-  "description": "Returns the y coordinate of the current feature.",
+  "description": "Returns the y coordinate of the current point feature.",
   "examples": [ { "expression":"$y", "returns":"42"}
   ]
 }
diff --git a/resources/function_help/json/x b/resources/function_help/json/x
index 03e72bf069f..1a6e72a3677 100644
--- a/resources/function_help/json/x
+++ b/resources/function_help/json/x
@@ -2,7 +2,7 @@
   "name": "x",
   "type": "function",
   "groups": ["GeometryGroup"],
-  "description": "Returns the x coordinate of a point geometry, or the x-coordinate of the centroid for a non-point geometry.",
+  "description": "Returns the x coordinate of a point geometry, or the x coordinate of the centroid for a non-point geometry.",
   "arguments": [ {"arg":"geom","description":"a geometry"}],
   "examples": [ { "expression":"x( geom_from_wkt( 'POINT(2 5)' ) )", "returns":"2"},
   { "expression":"x( $geometry )", "returns":"x coordinate of the current feature's centroid"}
diff --git a/resources/function_help/json/y b/resources/function_help/json/y
index a4e3fefc829..f97ea884866 100644
--- a/resources/function_help/json/y
+++ b/resources/function_help/json/y
@@ -2,7 +2,7 @@
   "name": "y",
   "type": "function",
   "groups": ["GeometryGroup"],
-  "description": "Returns the y coordinate of a point geometry, or the y-coordinate of the centroid for a non-point geometry.",
+  "description": "Returns the y coordinate of a point geometry, or the y coordinate of the centroid for a non-point geometry.",
   "arguments": [ {"arg":"geom","description":"a geometry"}],
   "examples": [ { "expression":"y( geom_from_wkt( 'POINT(2 5)' ) )", "returns":"5"},
   { "expression":"y( $geometry )", "returns":"y coordinate of the current feature's centroid"}
diff --git a/resources/function_help/json/z b/resources/function_help/json/z
index 3d11726c7d6..080084b1629 100644
--- a/resources/function_help/json/z
+++ b/resources/function_help/json/z
@@ -2,7 +2,7 @@
   "name": "z",
   "type": "function",
   "groups": ["GeometryGroup"],
-  "description": "Returns the z coordinate of a point geometry.",
+  "description": "Returns the z coordinate of a point geometry, or Null if the geometry has no z value.",
   "arguments": [ {"arg":"geom","description":"a point geometry"}],
   "examples": [ { "expression":"z( geom_from_wkt( 'POINTZ(2 5 7)' ) )", "returns":"7"}
   ]
diff --git a/resources/function_help/json/z_max b/resources/function_help/json/z_max
index 565ab9911ec..117b794bbdc 100644
--- a/resources/function_help/json/z_max
+++ b/resources/function_help/json/z_max
@@ -2,9 +2,12 @@
   "name": "z_max",
   "type": "function",
   "groups": ["GeometryGroup"],
-  "description": "Returns the maximum z coordinate of a geometry.",
+  "description": "Returns the maximum z coordinate of a geometry, or Null if the geometry has no z value.",
   "arguments": [ {"arg":"geometry","description":"a geometry with z coordinate"}],
   "examples": [ { "expression":"z_max( geom_from_wkt( 'POINT ( 0 0 1 )' ) )", "returns":"1"},
-                { "expression":"z_max( make_line( make_point( 0,0,0 ), make_point( -1,-1,-2 ) ) )", "returns":"0"}
+                { "expression":"z_max( geom_from_wkt( 'MULTIPOINT ( 0 0 1 , 1 1 3 )' ) )", "returns":"3"},
+                { "expression":"z_max( make_line( make_point( 0,0,0 ), make_point( -1,-1,-2 ) ) )", "returns":"0"},
+                { "expression":"z_max( geom_from_wkt( 'LINESTRING( 0 0 0, 1 0 2, 1 1 -1 )' ) ), "returns":"2"},
+                { "expression":"z_max( geom_from_wkt( 'POINT ( 0 0 )' ) )", "returns":"Null"}
   ]
 }
diff --git a/resources/function_help/json/z_min b/resources/function_help/json/z_min
index d2057bbaad5..9fa10b027a4 100644
--- a/resources/function_help/json/z_min
+++ b/resources/function_help/json/z_min
@@ -2,9 +2,12 @@
   "name": "z_min",
   "type": "function",
   "groups": ["GeometryGroup"],
-  "description": "Returns the minimum z coordinate of a geometry.",
+  "description": "Returns the minimum z coordinate of a geometry, or Null if the geometry has no z value.",
   "arguments": [ {"arg":"geometry","description":"a geometry with z coordinate"}],
   "examples": [ { "expression":"z_min( geom_from_wkt( 'POINT ( 0 0 1 )' ) )", "returns":"1"},
-                { "expression":"z_min( make_line( make_point( 0,0,0 ), make_point( -1,-1,-2 ) ) )", "returns":"-2"}
+                { "expression":"z_min( geom_from_wkt( 'MULTIPOINT ( 0 0 1 , 1 1 3 )' ) )", "returns":"1"},
+                { "expression":"z_min( make_line( make_point( 0,0,0 ), make_point( -1,-1,-2 ) ) )", "returns":"-2"},
+                { "expression":"z_min( geom_from_wkt( 'LINESTRING( 0 0 0, 1 0 2, 1 1 -1 )' ) ), "returns":"-1"},
+                { "expression":"z_min( geom_from_wkt( 'POINT ( 0 0 )' ) )", "returns":"Null"}
   ]
 }