📝 Update More API Document

docs/api/text-style.md

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+---
+name: text-style
+group: api
+category: formatter
+update-time: 20260520
+description: Create a reusable text style used by style tags and formatter config helpers.
+key-word:
+    - style
+    - formatter
+    - color
+    - public
+---
+
+## Text-style
+
+Create a `TextStyle` describing foreground color, background color, and emphasis flags such as bold or underline. This helper is the basic style value used by formatter style tags and config-driven formatter settings.
+
+### Interface
+
+```moonbit
+pub fn text_style(
+  fg~ : String? = None,
+  bg~ : String? = None,
+  bold~ : Bool = false,
+  dim~ : Bool = false,
+  italic~ : Bool = false,
+  underline~ : Bool = false,
+) -> TextStyle {
+```
+
+#### input
+
+- `fg : String?` - Optional foreground color, usually a named color or hex string.
+- `bg : String?` - Optional background color.
+- `bold : Bool` - Whether bold emphasis is enabled.
+- `dim : Bool` - Whether dim emphasis is enabled.
+- `italic : Bool` - Whether italic emphasis is enabled.
+- `underline : Bool` - Whether underline emphasis is enabled.
+
+#### output
+
+- `TextStyle` - Reusable style value.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- This helper creates a plain style value; it does not register tags by itself.
+- The returned style is commonly used in `style_tag_registry()` and `TextFormatterConfig::new(style_tags=...)`.
+- Color interpretation still depends on formatter color settings and runtime support.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need A Reusable Custom Tag Style
+
+When a formatter should define a named style tag:
+```moonbit
+let accent = text_style(fg=Some("#4cc9f0"), bold=true)
+```
+
+In this example, `accent` becomes a reusable style value that can be attached to a style tag registry or config map.
+
+### Error Case
+
+e.g.:
+- If a style uses colors but the formatter disables markup or color output, visible rendering may not reflect the full style.
+
+- This helper does not validate higher-level tag naming because it only creates the style value itself.
+
+### Notes
+
+1. This is the basic building block for style-tag customization.
+
+2. Use `style_tag_registry()` when you need named tags rather than a raw style value.