diff --git a/style.lua b/style.lua
index c0a646e9d..c1710f3fa 100644
--- a/style.lua
+++ b/style.lua
@@ -1,8 +1,12 @@
+-- For documentation of Lua tag transformations, see docs/lua.md.
+
+-- Objects without any of the following keys will be treated as polygon
 polygon_keys = { 'building', 'landuse', 'amenity', 'harbour', 'historic', 'leisure', 
       'man_made', 'military', 'natural', 'office', 'place', 'power',
       'public_transport', 'shop', 'sport', 'tourism', 'waterway',
       'wetland', 'water', 'aeroway' }
 
+-- Objects without any of the following keys will be deleted
 generic_keys = {'access','addr:housename','addr:housenumber','addr:interpolation','admin_level','aerialway','aeroway','amenity','area','barrier',
    'bicycle','brand','bridge','boundary','building','capital','construction','covered','culvert','cutting','denomination','disused','ele',
    'embarkment','foot','generation:source','harbour','highway','historic','hours','intermittent','junction','landuse','layer','leisure','lock',
@@ -10,26 +14,37 @@ generic_keys = {'access','addr:housename','addr:housenumber','addr:interpolation
    'railway','ref','religion','route','service','shop','sport','surface','toll','tourism','tower:type', 'tracktype','tunnel','water','waterway',
    'wetland','width','wood','type'}
 
+-- The following keys will be deleted
+delete_tags = { 'FIXME', 'note', 'source' }
+
+-- Array used to specify z_order per key/value combination.
+-- Each element has the form {key, value, z_order, is_road}.
+-- If is_road=1, the object will be added to planet_osm_roads.
+zordering_tags = {{ 'railway', nil, 5, 1}, { 'boundary', 'administrative', 0, 1}, 
+   { 'bridge', 'yes', 10, 0 }, { 'bridge', 'true', 10, 0 }, { 'bridge', 1, 10, 0 },
+   { 'tunnel', 'yes', -10, 0}, { 'tunnel', 'true', -10, 0}, { 'tunnel', 1, -10, 0}, 
+   { 'highway', 'minor', 3, 0}, { 'highway', 'road', 3, 0 }, { 'highway', 'unclassified', 3, 0 },
+   { 'highway', 'residential', 3, 0 }, { 'highway', 'tertiary_link', 4, 0}, { 'highway', 'tertiary', 4, 0},
+   { 'highway', 'secondary_link', 6, 1}, { 'highway', 'secondary', 6, 1},
+   { 'highway', 'primary_link', 7, 1}, { 'highway', 'primary', 7, 1},
+   { 'highway', 'trunk_link', 8, 1}, { 'highway', 'trunk', 8, 1},
+   { 'highway', 'motorway_link', 9, 1}, { 'highway', 'motorway', 9, 1},
+}
+
 function add_z_order(keyvalues)
+   -- The default z_order is 0
    z_order = 0
+
+   -- Add the value of the layer key times 10 to z_order
    if (keyvalues["layer"] ~= nil and tonumber(keyvalues["layer"])) then
       z_order = 10*keyvalues["layer"]
    end
 
-   
-   zordering_tags = {{ 'railway', nil, 5, 1}, { 'boundary', 'administrative', 0, 1}, 
-      { 'bridge', 'yes', 10, 0 }, { 'bridge', 'true', 10, 0 }, { 'bridge', 1, 10, 0 },
-      { 'tunnel', 'yes', -10, 0}, { 'tunnel', 'true', -10, 0}, { 'tunnel', 1, -10, 0}, 
-      { 'highway', 'minor', 3, 0}, { 'highway', 'road', 3, 0 }, { 'highway', 'unclassified', 3, 0 },
-      { 'highway', 'residential', 3, 0 }, { 'highway', 'tertiary_link', 4, 0}, { 'highway', 'tertiary', 4, 0},
-      { 'highway', 'secondary_link', 6, 1}, { 'highway', 'secondary', 6, 1},
-      { 'highway', 'primary_link', 7, 1}, { 'highway', 'primary', 7, 1},
-      { 'highway', 'trunk_link', 8, 1}, { 'highway', 'trunk', 8, 1},
-      { 'highway', 'motorway_link', 9, 1}, { 'highway', 'motorway', 9, 1},
-}
-   
+   -- Increase or decrease z_order based on the specific key/value combination as specified in zordering_tags
    for i,k in ipairs(zordering_tags) do
+      -- If the value in zordering_tags is specified, match key and value. Otherwise, match key only.
       if ((k[2]  and keyvalues[k[1]] == k[2]) or (k[2] == nil and keyvalues[k[1]] ~= nil)) then
+         -- If the fourth component of the element of zordering_tags is 1, add the object to planet_osm_roads
          if (k[4] == 1) then
             roads = 1
          end
@@ -37,27 +52,29 @@ function add_z_order(keyvalues)
       end
    end
 
+   -- Add z_order as key/value combination
    keyvalues["z_order"] = z_order
 
    return keyvalues, roads
-
 end
 
-function filter_tags_generic(keyvalues, nokeys)
-   filter = 0
-   tagcount = 0
+-- Filtering on nodes, ways, and relations
+function filter_tags_generic(keyvalues, numberofkeys)
+   filter = 0   -- Will object be filtered out?
 
-   if nokeys == 0 then
+   -- Filter out objects with 0 tags
+   if numberofkeys == 0 then
       filter = 1
       return filter, keyvalues
    end
 
-   delete_tags = { 'FIXME', 'note', 'source' }
-
+   -- Delete tags listed in delete_tags
    for i,k in ipairs(delete_tags) do
       keyvalues[k] = nil
    end
    
+   -- Filter out objects that do not have any of the keys in generic_keys
+   tagcount = 0
    for k,v in pairs(keyvalues) do
       for i, k2 in ipairs(generic_keys) do if k2 == k then tagcount = tagcount + 1; end end
    end
@@ -68,17 +85,20 @@ function filter_tags_generic(keyvalues, nokeys)
    return filter, keyvalues
 end
 
-function filter_tags_node (keyvalues, nokeys)
-   return filter_tags_generic(keyvalues, nokeys)
+-- Filtering on nodes
+function filter_tags_node (keyvalues, numberofkeys)
+   return filter_tags_generic(keyvalues, numberofkeys)
 end
 
-function filter_basic_tags_rel (keyvalues, nokeys)
-
-   filter, keyvalues = filter_tags_generic(keyvalues, nokeys)
+-- Filtering on relations
+function filter_basic_tags_rel (keyvalues, numberofkeys)
+   -- Filter out objects that are filtered out by filter_tags_generic
+   filter, keyvalues = filter_tags_generic(keyvalues, numberofkeys)
    if filter == 1 then
       return filter, keyvalues
    end
 
+   -- Filter out all relations except route, multipolygon and boundary relations
    if ((keyvalues["type"] ~= "route") and (keyvalues["type"] ~= "multipolygon") and (keyvalues["type"] ~= "boundary")) then
       filter = 1
       return filter, keyvalues
@@ -87,66 +107,74 @@ function filter_basic_tags_rel (keyvalues, nokeys)
    return filter, keyvalues
 end
 
-function filter_tags_way (keyvalues, nokeys)
-   filter = 0
-   poly = 0
-   tagcount = 0
-   roads = 0
+-- Filtering on ways
+function filter_tags_way (keyvalues, numberofkeys)
+   filter = 0  -- Will object be filtered out?
+   polygon = 0 -- Will object be treated as polygon?
+   roads = 0   -- Will object be added to planet_osm_roads?
 
-   filter, keyvalues = filter_tags_generic(keyvalues, nokeys)
+   -- Filter out objects that are filtered out by filter_tags_generic
+   filter, keyvalues = filter_tags_generic(keyvalues, numberofkeys)
    if filter == 1 then
-      return filter, keyvalues, poly, roads
+      return filter, keyvalues, polygon, roads
    end
 
-
+  -- Treat objects with a key in polygon_keys as polygon
    for i,k in ipairs(polygon_keys) do
       if keyvalues[k] then
-         poly=1
+         polygon=1
          break
       end
    end
    
-
+   -- Treat objects tagged as area=yes, area=1, or area=true as polygon,
+   -- and treat objects tagged as area=no, area=0, or area=false not as polygon
    if ((keyvalues["area"] == "yes") or (keyvalues["area"] == "1") or (keyvalues["area"] == "true")) then
-      poly = 1;
+      polygon = 1;
    elseif ((keyvalues["area"] == "no") or (keyvalues["area"] == "0") or (keyvalues["area"] == "false")) then
-      poly = 0;
+      polygon = 0;
    end
 
+   -- Add z_order key/value combination and determine if the object should also be added to planet_osm_roads
    keyvalues, roads = add_z_order(keyvalues)
 
-
-   return filter, keyvalues, poly, roads
+   return filter, keyvalues, polygon, roads
 end
 
 function filter_tags_relation_member (keyvalues, keyvaluemembers, roles, membercount)
-   
-   filter = 0
-   boundary = 0
-   polygon = 0
-   roads = 0
-   membersuperseeded = {}
+   filter = 0     -- Will object be filtered out?
+   linestring = 0 -- Will object be treated as linestring?
+   polygon = 0    -- Will object be treated as polygon?
+   roads = 0      -- Will object be added to planet_osm_roads?
+   membersuperseded = {}
    for i = 1, membercount do
-      membersuperseeded[i] = 0
+      membersuperseded[i] = 0 -- Will member be ignored when handling areas?
    end
 
    type = keyvalues["type"]
+
+   -- Remove type key
    keyvalues["type"] = nil
   
-
+   -- Relations with type=boundary are treated as linestring
    if (type == "boundary") then
-      boundary = 1
+      linestring = 1
    end
+   -- Relations with type=multipolygon and boundary=* are treated as linestring
    if ((type == "multipolygon") and keyvalues["boundary"]) then
-      boundary = 1
+      linestring = 1
+   -- For multipolygons...
    elseif (type == "multipolygon") then
+      -- Treat as polygon
       polygon = 1
       polytagcount = 0;
+      -- Count the number of polygon tags of the object
       for i,k in ipairs(polygon_keys) do
          if keyvalues[k] then
             polytagcount = polytagcount + 1
          end
       end
+      -- If there are no polygon tags, add tags from all outer elements to the multipolygon itself
       if (polytagcount == 0) then
          for i = 1,membercount do
             if (roles[i] == "outer") then
@@ -156,23 +184,28 @@ function filter_tags_relation_member (keyvalues, keyvaluemembers, roles, memberc
             end
          end
       end
+      -- For any member of the multipolygon, set membersuperseded to 1 (i.e. don't deal with it as area as well),
+      -- except when the member has a key/value combination such that
+      --   1) the key occurs in generic_keys
+      --   2) the key/value combination is not also a key/value combination of the multipolygon itself
       for i = 1,membercount do
-         superseeded = 1
+         superseded = 1
          for k,v in pairs(keyvaluemembers[i]) do
             if ((keyvalues[k] == nil) or (keyvalues[k] ~= v)) then
                for j,k2 in ipairs(generic_keys) do
                   if (k == k2) then
-                     superseeded = 0;
+                     superseded = 0;
                      break
                   end
                end
             end
          end
-         membersuperseeded[i] = superseeded
+         membersuperseded[i] = superseded
       end
    end
 
+   -- Add z_order key/value combination and determine if the object should also be added to planet_osm_roads
    keyvalues, roads = add_z_order(keyvalues)
 
-   return filter, keyvalues, membersuperseeded, boundary, polygon, roads
+   return filter, keyvalues, membersuperseded, boundary, polygon, roads
 end