📝 document public config and level aliases

docs/api/sink-kind.md

@@ -0,0 +1,72 @@
+---
+name: sink-kind
+group: api
+category: config
+update-time: 20260613
+description: Public sink kind enum alias used by SinkConfig and config parsing.
+key-word:
+    - sink
+    - config
+    - alias
+    - public
+---
+
+## Sink-kind
+
+`SinkKind` is the public enum that selects which built-in sink shape a `SinkConfig` should build. It is a direct alias to the internal config enum, so config builders, JSON parsers, and sink serialization helpers all use the same small set of variants.
+
+### Interface
+
+```moonbit
+pub type SinkKind = @utils.SinkKind
+```
+
+#### output
+
+- `SinkKind` - Public sink selection enum with the variants `Console`, `JsonConsole`, `TextConsole`, and `File`.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- This is a type alias, not a wrapper or a new runtime sink implementation.
+- `SinkKind::Console` selects the basic text console sink.
+- `SinkKind::JsonConsole` selects JSON line output.
+- `SinkKind::TextConsole` selects text console output driven by `TextFormatterConfig`.
+- `SinkKind::File` selects file-backed output and requires a non-empty `path` during config parsing.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need To Build A File Sink Through Config
+
+When logger construction should be described entirely as config data:
+```moonbit
+let sink = SinkConfig::new(kind=SinkKind::File, path="app.log")
+let config = LoggerConfig::new(sink=sink)
+```
+
+In this example, the selected enum variant controls which built-in sink builder will be used.
+
+#### When Need Formatter-driven Console Output
+
+When the config should request text console formatting instead of the default console sink:
+```moonbit
+let sink = SinkConfig::new(kind=SinkKind::TextConsole)
+```
+
+In this example, the enum value makes the config intent explicit.
+
+### Error Case
+
+e.g.:
+- Unsupported sink kind text in parsed JSON raises `ConfigError`.
+
+- `SinkKind::File` without a non-empty `path` is rejected during config parsing.
+
+### Notes
+
+1. This enum is for config-driven sink selection, not for direct handwritten sink composition.
+
+2. Use concrete constructors such as `console_sink()` or `file_sink(...)` when building sinks in code instead of through `SinkConfig`.