📝 Update More API Document

docs/api/style-tag-registry.md

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+---
+name: style-tag-registry
+group: api
+category: formatter
+update-time: 20260520
+description: Create an empty style tag registry for custom formatter markup tags.
+key-word:
+    - style
+    - registry
+    - formatter
+    - public
+---
+
+## Style-tag-registry
+
+Create an empty `StyleTagRegistry` for custom formatter style tags. This is the starting point for defining named tags such as `accent` or aliases such as `danger`.
+
+### Interface
+
+```moonbit
+pub fn style_tag_registry() -> StyleTagRegistry {
+```
+
+#### output
+
+- `StyleTagRegistry` - Empty registry ready for `set_tag(...)` and alias operations.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The returned registry starts empty.
+- This helper is intended for runtime formatter customization in code.
+- Registries created here can be attached to `text_formatter(...)` through `with_style_tags(...)`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Custom Named Tags
+
+When formatter markup should define project-specific tag names:
+```moonbit
+let tags = style_tag_registry().set_tag("accent", fg=Some("#4cc9f0"), bold=true)
+```
+
+In this example, the registry becomes the container for custom named styles.
+
+### Error Case
+
+e.g.:
+- If the formatter never enables the relevant style markup mode, tags in the registry may remain unused.
+
+- An empty registry is valid, but it does not add any custom tags by itself.
+
+### Notes
+
+1. This helper creates a runtime registry, not a serializable config map.
+
+2. Use `default_style_tag_registry()` when you want the built-in tag set as a starting point.