Update doc

doc.go

@@ -1,2 +1,72 @@
-// Package opt implements methods for manage arguments of the command-line.
+// Package opt provides command-line argument parsing and management
+// for Go applications.
+//
+// Unlike Go's standard flag package which follows Plan 9 style (single
+// dash flags only), this package implements Linux-style argument parsing
+// with support for both short (-v) and long (--verbose) flags to match
+// common Unix/Linux command line conventions.
+//
+// Features:
+// - Parses command-line arguments into Go structs using struct tags
+// - Supports both short (-v) and long (--verbose) flag formats (Linux-style)
+// - Handles positional arguments with automatic ordering
+// - Provides default values through struct tags
+// - Generates help documentation automatically
+// - Supports grouped short flags (-abc equivalent to -a -b -c)
+// - Allows flag aliases through the alt tag
+//
+// Supported field types:
+// - Basic types: int, int8, int16, int32, int64
+// - Unsigned types: uint, uint8, uint16, uint32, uint64
+// - Floating point: float32, float64
+// - Other basic types: string, bool
+// - URL types: url.URL and *url.URL
+// - Arrays and slices of the above types
+//
+// Struct tags:
+// - opt: Defines the primary flag name (required)
+// - alt: Defines an alternative flag name (optional)
+// - def: Sets the default value (optional)
+// - sep: Specifies list separator for array/slice types (optional)
+// - help: Provides help text for documentation (optional)
+//
+// Special opt tag values:
+// - "?" : Field will store generated help text
+// - "[]": Field will store positional arguments
+// - "-" : Field will be ignored during parsing
+// - "0", "1", ...: Field will store specific positional argument
+//
+// Example usage:
+//
+//	type Args struct {
+//	    Host    string `opt:"host" alt:"H" def:"localhost" help:"server host address"`
+//	    Port    int    `opt:"p" alt:"port" def:"8080" help:"server port number"`
+//	    Debug   bool   `opt:"d" help:"enable debug mode"`
+//	    Config  string `opt:"c" help:"path to config file"`
+//	    Help    bool   `opt:"h" alt:"help" help:"show help information"`
+//	    DocText string `opt:"?"`
+//	}
+//
+//	func main() {
+//	    var args Args
+//	    if err := opt.Unmarshal(&args); err != nil {
+//	        log.Fatal(err)
+//	    }
+//	}
+//
+// Command line examples:
+//
+//	./app --host=localhost -p 8080 --debug
+//	./app -H 127.0.0.1 --port=8080 -d
+//	./app -h (displays help)
+//
+// Error handling:
+// - Returns errors for unknown flags
+// - Returns errors for invalid value types
+// - Returns errors for array/slice overflow
+// - Generates panic for invalid struct configuration
+//
+// Thread safety:
+// The package is safe to use from multiple goroutines
+// after initial configuration.
 package opt