docs: improve code documentation and comments

- Update comments for `BundleCfg` fields to include descriptions of their purposes
- Add detailed comments to `WithBundle` and `WithGetLngHandle` functions explaining their behavior and defaults
- Remove placeholder comments without descriptions

Signed-off-by: Bo-Yi Wu <[email protected]>

option.go

@@ -5,14 +5,14 @@ import (
 	"golang.org/x/text/language"
 )
 
-// BundleCfg ...
+// BundleCfg represents the configuration options for an i18n bundle.
 type BundleCfg struct {
-	DefaultLanguage  language.Tag
-	FormatBundleFile string
-	AcceptLanguage   []language.Tag
-	RootPath         string
-	UnmarshalFunc    i18n.UnmarshalFunc
-	Loader           Loader
+	DefaultLanguage  language.Tag       // DefaultLanguage specifies the default language for the bundle.
+	FormatBundleFile string             // FormatBundleFile specifies the file format for the bundle.
+	AcceptLanguage   []language.Tag     // AcceptLanguage specifies the accepted languages for the bundle.
+	RootPath         string             // RootPath specifies the root path for the bundle.
+	UnmarshalFunc    i18n.UnmarshalFunc // UnmarshalFunc specifies the function used for unmarshaling bundle files.
+	Loader           Loader             // Loader specifies the loader for loading bundle files.
 }
 
 type Loader interface {
@@ -23,7 +23,8 @@ type LoaderFunc func(path string) ([]byte, error)
 
 func (f LoaderFunc) LoadMessage(path string) ([]byte, error) { return f(path) }
 
-// WithBundle ...
+// WithBundle returns an Option that sets the bundle configuration for GinI18n.
+// If the loader is not provided in the BundleCfg, the defaultLoader will be used.
 func WithBundle(config *BundleCfg) Option {
 	return func(g GinI18n) {
 		if config.Loader == nil {
@@ -33,7 +34,9 @@ func WithBundle(config *BundleCfg) Option {
 	}
 }
 
-// WithGetLngHandle ...
+// WithGetLngHandle sets the handler function for retrieving the current language.
+// The provided handler function should accept a GinI18n instance and return the current language as a string.
+// This option allows you to customize how the current language is determined.
 func WithGetLngHandle(handler GetLngHandler) Option {
 	return func(g GinI18n) {
 		g.setGetLngHandler(handler)