Leading zeros is not allowed in rfc7159

[zycbobby]

As I check in https://datatracker.ietf.org/doc/html/rfc7159,

The representation of numbers is similar to that used in most
programming languages. A number is represented in base 10 using
decimal digits. It contains an integer component that may be
prefixed with an optional minus sign, which may be followed by a
fraction part and/or an exponent part. Leading zeros are not
allowed.

but it looks like github.com/ugorji/go can parse leading zero number as a valid one

package main

import (
	"fmt"

	"github.com/ugorji/go/codec"
)

type A struct {
	Score float64 `json:"score"`
}

func main() {
	str := `
	{
		"score": 08
	}`

	a := A{}

	codec.NewDecoderBytes([]byte(str), new(codec.JsonHandle)).Decode(&a)

	fmt.Println(a.Score)
}

it outputs

╰─$ go run main.go
8

I am using

module json

go 1.18

require github.com/ugorji/go/codec v1.2.12

It(this bug/feature) is not that important to my project, I am just wondering if there is some consideration in implementation lead to this bug/feature, which can achieve a better performance for json encode/decode?