You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: tag.go
    path of file: ./repos/teller/vendor/github.com/alecthomas/kong
    
    the code of the file until where you have to start completion: package kong

import (
	"fmt"
	"reflect"
	"strconv"
	"strings"
	"unicode/utf8"
)

// Tag represents the parsed state of Kong tags in a struct field tag.
type Tag struct {
	Ignored     bool // Field is ignored by Kong. ie. kong:"-"
	Cmd         bool
	Arg         bool
	Required    bool
	Optional    bool
	Name        string
	Help        string
	Type        string
	Default     string
	Format      string
	PlaceHolder string
	Env         string
	Short       rune
	Hidden      bool
	Sep         rune
	MapSep      rune
	Enum        string
	Group       string
	Xor         string
	Vars        Vars
	Prefix      string // Optional prefix on anonymous structs. All sub-flags will have this prefix.
	Embed       bool
	Aliases     []string

	// Storage for all tag keys for arbitrary lookups.
	items map[string][]string
}

type tagChars struct {
	sep, quote, assign rune
}

var kongChars = tagChars{sep: ',', quote: '\'', assign: '='}
var bareChars = tagChars{sep: ' '
    
func parseTag(fv reflect.Value, ft reflect.StructField) *Tag {
	if ft.Tag.Get("kong") == "-" {
		t := newEmptyTag()
		t.Ignored = true
		return t
	}
	t := &Tag{
		items: parseTagItems(getTagInfo(ft)),
	}
	t.Cmd = t.Has("cmd")
	t.Arg = t.Has("arg")
	required := t.Has("required")
	optional := t.Has("optional")
	if required && optional {
		fail("can't specify both required and optional")
	}
	t.Required = required
	t.Optional = optional
	t.Default = t.Get("default")
	// Arguments with defaults are always optional.
	if t.Arg && t.Default != "" {
		t.Optional = true
	}
	t.Name = t.Get("name")
	t.Help = t.Get("help")
	t.Type = t.Get("type")
	t.Env = t.Get("env")
	t.Short, _ = t.GetRune("short")
	t.Hidden = t.Has("hidden")
	t.Format = t.Get("format")
	t.Sep, _ = t.GetSep("sep", ',')
	t.MapSep, _ = t.GetSep("mapsep", ';')
	t.Group = t.Get("group")
	t.Xor = t.Get("xor")
	t.Prefix = t.Get("prefix")
	t.Embed = t.Has("embed")
	splitFn := func(r rune) bool {
		return r == ',' || r == ' '
	}
	aliases := t.Get("aliases")
	if len(aliases) > 0 {
		t.Aliases = append(t.Aliases, strings.FieldsFunc(aliases, splitFn)...)
	}
	t.Vars = Vars{}
	for _, set := range t.GetAll("set") {
		parts := strings.SplitN(set, "=", 2)
		if len(parts) == 0 {
			fail("set should be in the form key=value but got %q", set)
		}
		t.Vars[parts[0]] = parts[1]
	}
	t.PlaceHolder = t.Get("placeholder")
	if t.PlaceHolder == "" {
		t.PlaceHolder = strings.ToUpper(dashedString(fv.Type().Name()))
	}
	t.Enum = t.Get("enum")
	return t
}