Added a whole lot of rudimentary comments, also importing selects the last imported mod if possible.

Penumbra/Meta/Files/ImcExtensions.cs

@@ -14,6 +14,8 @@ namespace Penumbra.Meta.Files
         { }
     }
 
+    // Imc files are already supported in Lumina, but changing the provided data is not supported.
+    // We use reflection and extension methods to support changing the data of a given Imc file.
     public static class ImcExtensions
     {
         public static ulong ToInteger( this ImcFile.ImageChangeData imc )

Penumbra/Meta/Files/MetaDefaults.cs

@@ -9,6 +9,8 @@ using Penumbra.Util;
 
 namespace Penumbra.Meta.Files
 {
+    // This class manages the default meta files obtained via lumina from the game files themselves.
+    // On first call, the default version of any supported file will be cached and can be returned without reparsing.
     public class MetaDefaults
     {
         private readonly DalamudPluginInterface _pi;
@@ -107,6 +109,7 @@ namespace Penumbra.Meta.Files
         private FileResource FetchFile( string name )
             => _pi.Data.GetFile( name );
 
+        // Check that a given meta manipulation is an actual change to the default value. We don't need to keep changes to default.
         public bool CheckAgainstDefault( MetaManipulation m )
         {
             return m.Type switch
@@ -129,6 +132,7 @@ namespace Penumbra.Meta.Files
             };
         }
 
+        // Create a deep copy of a default file as a new file.
         public object? CreateNewFile( MetaManipulation m )
         {
             return m.Type switch

Penumbra/Meta/Files/MetaFilenames.cs

@@ -4,6 +4,7 @@ using Penumbra.Util;
 
 namespace Penumbra.Meta.Files
 {
+    // Contains all filenames for meta changes depending on their parameters.
     public static class MetaFileNames
     {
         public static GamePath Eqp()

Penumbra/Meta/Identifier.cs

@@ -1,6 +1,10 @@
 using System.Runtime.InteropServices;
 using Penumbra.Game.Enums;
 
+
+// A struct for each type of meta change that contains all relevant information,
+// to uniquely identify the corresponding file and location for the change.
+// The first byte is guaranteed to be the MetaType enum for each case.
 namespace Penumbra.Meta
 {
     public enum MetaType : byte

Penumbra/Meta/MetaManipulation.cs

@@ -12,6 +12,7 @@ using ImcFile = Lumina.Data.Files.ImcFile;
 
 namespace Penumbra.Meta
 {
+    // Write a single meta manipulation as a Base64string of the 16 bytes defining it.
     public class MetaManipulationConverter : JsonConverter< MetaManipulation >
     {
         public override void WriteJson( JsonWriter writer, MetaManipulation manip, JsonSerializer serializer )
@@ -38,6 +39,10 @@ namespace Penumbra.Meta
         }
     }
 
+    // A MetaManipulation is a union of a type of Identifier (first 8 bytes, cf. Identifier.cs)
+    // and the appropriate Value to change the meta entry to (the other 8 bytes).
+    // Its comparison for sorting and hashes depends only on the identifier.
+    // The first byte is guaranteed to be a MetaType enum value in any case, so Type can always be read.
     [StructLayout( LayoutKind.Explicit )]
     [JsonConverter( typeof( MetaManipulationConverter ) )]
     public struct MetaManipulation : IComparable
@@ -219,11 +224,11 @@ namespace Penumbra.Meta
         {
             return Type switch
             {
-                MetaType.Eqp  => $"EQP - {EqpIdentifier}",
-                MetaType.Eqdp => $"EQDP - {EqdpIdentifier}",
-                MetaType.Est  => $"EST - {EstIdentifier}",
-                MetaType.Gmp  => $"GMP - {GmpIdentifier}",
-                MetaType.Imc  => $"IMC - {ImcIdentifier}",
+                MetaType.Eqp  => EqpIdentifier.ToString(),
+                MetaType.Eqdp => EqdpIdentifier.ToString(),
+                MetaType.Est  => EstIdentifier.ToString(),
+                MetaType.Gmp  => GmpIdentifier.ToString(),
+                MetaType.Imc  => ImcIdentifier.ToString(),
                 _             => throw new InvalidEnumArgumentException(),
             };
         }