From a5b549a94fcaf57c719b579830b1c460f5e03e8a Mon Sep 17 00:00:00 2001
From: bohan <bohan-zhang@foxmail.com>
Date: Fri, 29 Nov 2024 11:54:33 +0800
Subject: [PATCH] docs: introduce primary param in label

---
 README.md | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/README.md b/README.md
index 646047c..74148d7 100644
--- a/README.md
+++ b/README.md
@@ -51,6 +51,7 @@ diagnostic error code: ruget::api::bad_json
   - [... handler options](#-handler-options)
   - [... dynamic diagnostics](#-dynamic-diagnostics)
   - [... syntax highlighting](#-syntax-highlighting)
+  - [... primary label](#-primary-label)
   - [... collection of labels](#-collection-of-labels)
 - [Acknowledgements](#acknowledgements)
 - [License](#license)
@@ -689,6 +690,37 @@ trait to [`MietteHandlerOpts`] by calling the
 [`with_syntax_highlighting`](MietteHandlerOpts::with_syntax_highlighting)
 method. See the [`highlighters`] module docs for more details.
 
+#### ... primary label
+
+You can use the `primary` parameter to `label` to indicate that the label
+is the primary label.
+
+```rust
+#[derive(Debug, Diagnostic, Error)]
+#[error("oops!")]
+struct MyError {
+    #[label(primary, "main issue")]
+    primary_span: SourceSpan,
+
+    #[label("other label")]
+    other_span: SourceSpan,
+}
+```
+
+The `primary` parameter can be used at most once:
+
+```rust
+#[derive(Debug, Diagnostic, Error)]
+#[error("oops!")]
+struct MyError {
+    #[label(primary, "main issue")]
+    primary_span: SourceSpan,
+
+    #[label(primary, "other label")] // Error: Cannot have more than one primary label.
+    other_span: SourceSpan,
+}
+```
+
 #### ... collection of labels
 
 When the number of labels is unknown, you can use a collection of `SourceSpan`