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: parser.go
    path of file: ./repos/cel-go/vendor/golang.org/x/text/internal/format
    
    the code of the file until where you have to start completion: // Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package format

import (
	"reflect"
	"unicode/utf8"
)

// A Parser parses a format string. The result from the parse are set in the
// str
    
func (p *Parser) updateArgNumber(format string, i int) (newi int, found bool) {
	if len(format) <= i || format[i] != '[' {
		return i, false
	}
	p.Reordered = true
	index, wid, ok := parseArgNumber(format[i:])
	if ok && 0 <= index && index < len(p.Args) {
		p.ArgNum = index
		return i + wid, true
	}
	p.goodArgNum = false
	return i + wid, ok
}