add a docs page

docs/source/atproto_client/string_formats.md

@@ -0,0 +1,160 @@
+## String Formats
+
+The AT Protocol defines several string formats that are used throughout the protocol. This page describes these formats and how to validate them in your code.
+
+### Overview
+
+The SDK provides optional strict validation for AT Protocol string formats. By default, validation is disabled for performance reasons, but you can enable it when needed.
+
+### Validation Examples
+
+Using `Handle` as an example, here are the four main validation cases:
+
+```python
+from pydantic import TypeAdapter
+from atproto_client.models.string_formats import Handle
+
+HandleAdapter = TypeAdapter(Handle)
+
+# Case 1: Valid handle without validation (passes)
+handle1 = HandleAdapter.validate_python("alice.bsky.social")
+
+# Case 2: Valid handle with validation (passes)
+handle2 = HandleAdapter.validate_python(
+    "alice.bsky.social",
+    context={"strict_string_format": True}
+)
+
+# Case 3: Invalid handle without validation (passes)
+handle3 = HandleAdapter.validate_python("not a valid handle!")
+
+# Case 4: Invalid handle with validation (raises ValidationError)
+try:
+    HandleAdapter.validate_python(
+        "not a valid handle!",
+        context={"strict_string_format": True}
+    )
+except ValidationError as e:
+    print("Validation failed:", e)
+```
+
+### Supported String Formats
+
+The SDK supports validation of the following string formats:
+
+:::{attention}
+These formats are a working empirical understanding of the required formats based on the following resources:
+
+- https://atproto.com/specs/lexicon
+
+- https://github.com/bluesky-social/atproto/tree/main/interop-test-files/syntax
+
+:::
+
+
+#### Handle
+A handle must be a valid domain name (e.g., `user.bsky.social`):
+- 2+ segments separated by dots
+- ASCII alphanumeric characters and hyphens only
+- 1-63 chars per segment
+- Max 253 chars total
+- Last segment cannot start with a digit
+
+#### DID (Decentralized Identifier)
+A DID follows the pattern `did:method:identifier`:
+- Method must be lowercase letters
+- Identifier allows alphanumeric chars, dots, underscores, hyphens, and percent
+- Max 2KB length
+- No /?#[]@ characters allowed
+
+#### NSID (Namespaced Identifier)
+An NSID must have:
+- 3+ segments separated by dots
+- Reversed domain name (lowercase alphanumeric + hyphen)
+- Name segment (letters only)
+- Max 317 chars total
+- No segments ending in numbers
+- No @_*#! special characters
+- Max 63 chars per segment
+
+#### AT-URI
+An AT-URI must follow the pattern `at://authority/collection/record-key`:
+- Starts with `at://`
+- Contains handle or DID
+- Optional /collection/record-key path
+- Max 8KB length
+- No query parameters or fragments
+
+#### CID (Content Identifier)
+Must be:
+- Minimum 8 characters
+- Alphanumeric characters and plus signs only
+
+#### DateTime
+Requirements:
+- Must use uppercase T as time separator
+- Must include seconds (HH:MM:SS)
+- Must have timezone (Z or ±HH:MM)
+- No -00:00 timezone allowed
+- Valid fractional seconds format if used
+- No whitespace allowed
+
+#### TID (Temporal ID)
+Must be:
+- Exactly 13 characters
+- Only lowercase letters and numbers 2-7
+- First byte's high bit (0x40) must be 0
+
+#### Record Key
+A record key must:
+- Be 1-512 characters
+- Contain only alphanumeric chars, dots, underscores, colons, tildes, or hyphens
+- Not be "." or ".."
+
+#### URI
+Requirements:
+- Must have a scheme starting with a letter
+- Must have authority (netloc) or path/query/fragment
+- Max 8KB length
+- No spaces allowed
+- Must follow RFC-3986 format
+
+#### Language
+Must match pattern:
+- 2-3 letter language code or 'i'
+- Optional subtag with alphanumeric chars and hyphens
+
+### Using Validation in Your Code
+
+There are two ways to enable validation:
+
+1. Using `get_or_create` with `strict_string_format=True`:
+
+```python
+from atproto_client.models.utils import get_or_create
+from atproto_client.models.string_formats import Handle
+from pydantic import BaseModel
+
+class MyModel(BaseModel):
+    handle: Handle
+
+data = {"handle": "alice.bsky.social"}
+model = get_or_create(data, MyModel, strict_string_format=True)
+```
+
+2. Using Pydantic's validation context:
+
+```python
+from pydantic import BaseModel
+from atproto_client.models.string_formats import Handle
+
+class MyModel(BaseModel):
+    handle: Handle
+
+model = MyModel.model_validate(
+    {"handle": "alice.bsky.social"},
+    context={"strict_string_format": True}
+)
+```
+
+When validation is disabled (the default), any string value will be accepted. When enabled, the values must conform to the above validation rules, or else a `ValidationError` will be raised.

packages/atproto_client/models/string_formats.py

@@ -5,8 +5,6 @@
 - https://atproto.com/specs/lexicon
 
 - https://github.com/bluesky-social/atproto/tree/main/interop-test-files/syntax
-
-see https://github.com/MarshalX/atproto/pull/406 for more details.
 """
 
 import re