Partial way to unifying nixos and home-manager modules

lib/modules.nix

@@ -6,6 +6,10 @@ let
   inherit (self.attrs) mapFilterAttrs;
 in
 rec {
+  # Returns an attribute set with the keys being the files in a directory
+  # and the values a function applied to their paths
+  # Only *.nix files and directories with a default.nix file are considered.
+  # The ".nix" suffix is removed from the keys of the attribute set.
   mapModules = dir: fn:
     mapFilterAttrs
       (n: v:
@@ -22,9 +26,14 @@ rec {
         else nameValuePair "" null)
       (readDir dir);
 
+  # Like mapModules above, but it just returns the values
+  # (map the function fn over the files in a directory)
   mapModules' = dir: fn:
     attrValues (mapModules dir fn);
 
+  # Like mapModules, but recursive. That is, if there is a directory, the
+  # value will be another attribute set with its contents as keys and the funcion
+  # applied to them as values.
   mapModulesRec = dir: fn:
     mapFilterAttrs
       (n: v:
@@ -39,6 +48,9 @@ rec {
         else nameValuePair "" null)
       (readDir dir);
 
+  # Like mapModulesRec but flattened and only the values. That is, it returns a list
+  # with fn applied to all *.nix files within the directory and subdirectories
+  # excluding default.nix files.
   mapModulesRec' = dir: fn:
     let
       dirs =