Improve documentation and modernize type hints

src/rp/detect.py

@@ -60,6 +60,23 @@ def detect_type(
     content: str | None = None,
     explicit_type: str | None = None,
 ) -> str:
+    """Detect the file type for syntax highlighting.
+
+    Detection priority:
+    1. Explicit type if provided
+    2. Filename-based mapping (for example, Dockerfile)
+    3. Extension-based mapping
+    4. JSON if content starts with '{' or '[' and parses successfully
+    5. Fallback to 'text'
+
+    Args:
+        path: File path for filename and extension detection.
+        content: File content for JSON detection.
+        explicit_type: Override auto-detection with explicit type.
+
+    Returns:
+        Pygments lexer name for the detected file type.
+    """
     if explicit_type is not None:
         return explicit_type