docs: Add plugin codecs guide and fix codec notation

mkdocs.yaml

@@ -74,6 +74,7 @@ nav:
       - Object Storage:
           - Use Object Storage: how-to/use-object-storage.md
           - Use NPY Codec: how-to/use-npy-codec.md
+          - Use Plugin Codecs: how-to/use-plugin-codecs.md
           - Create Custom Codecs: how-to/create-custom-codec.md
           - Manage Large Data: how-to/manage-large-data.md
           - Clean Up Storage: how-to/garbage-collection.md

src/explanation/custom-codecs.md

@@ -334,3 +334,12 @@ Custom codecs enable:
 
 The codec system makes DataJoint extensible to any scientific domain without
 modifying the core framework.
+
+## Before Creating Your Own
+
+Check for existing plugin codecs that may already solve your needs:
+
+- **[dj-zarr-codecs](https://github.com/datajoint/dj-zarr-codecs)** — General numpy arrays with Zarr storage
+- **[dj-photon-codecs](https://github.com/datajoint/dj-photon-codecs)** — Photon-limited movies with Anscombe transformation and compression
+
+See the [Use Plugin Codecs](../how-to/use-plugin-codecs.md) guide for installation and usage of existing codec packages. Creating a custom codec is straightforward, but reusing existing ones saves time and ensures compatibility.

src/explanation/type-system.md

@@ -111,7 +111,22 @@ Codecs provide `encode()`/`decode()` semantics for complex Python objects.
 
 ### `<blob>` — Serialized Python Objects
 
-Stores NumPy arrays, dicts, lists, and other Python objects.
+Stores NumPy arrays, dicts, lists, and other Python objects using DataJoint's custom binary serialization format.
+
+**Serialization format:**
+- **Protocol headers**:
+  - `mYm` — MATLAB-compatible format (see [mYm on MATLAB FileExchange](https://www.mathworks.com/matlabcentral/fileexchange/81208-mym) and [mym on GitHub](https://github.com/datajoint/mym))
+  - `dj0` — Python-extended format supporting additional types
+- **Optional compression**: zlib compression for data > 1KB
+- **Type-specific encoding**: Each Python type has a specific serialization code
+- **Version detection**: Protocol header embedded in blob enables format detection
+
+**Supported types:**
+- NumPy arrays (numeric, structured, recarrays)
+- Collections (dict, list, tuple, set)
+- Scalars (int, float, bool, complex, str, bytes)
+- Date/time objects (datetime, date, time)
+- UUID, Decimal
 
 ```python
 class Results(dj.Computed):
@@ -124,6 +139,10 @@ class Results(dj.Computed):
     """
 ```
 
+**Storage modes:**
+- `<blob>` — Stored in database as LONGBLOB (up to ~1GB depending on MySQL config)
+- `<blob@>` — Stored externally via `<hash@>` with MD5 deduplication
+
 ### `<attach>` — File Attachments
 
 Stores files with filename preserved.

src/how-to/index.md

@@ -42,6 +42,7 @@ they assume you understand the basics and focus on getting things done.
 - [Object Storage Overview](object-storage-overview.md) — Navigation guide for all storage docs
 - [Choose a Storage Type](choose-storage-type.md) — Decision guide for codecs
 - [Use Object Storage](use-object-storage.md) — When and how
+- [Use Plugin Codecs](use-plugin-codecs.md) — Install codec packages via entry points
 - [Create Custom Codecs](create-custom-codec.md) — Domain-specific types
 - [Manage Large Data](manage-large-data.md) — Blobs, streaming, efficiency
 - [Clean Up External Storage](garbage-collection.md) — Garbage collection