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: decoder.go
    path of file: ./repos/sonic/util/pageparser/metadecoders
    
    the code of the file until where you have to start completion: // Copyright 2018 The Hugo Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package metadecoders

import (
	"bytes"
	"encoding/csv"
	"encoding/json"
	"fmt"
	"strings"

	xml "github.com/clbanning/mxj/v2"
	toml "github.com/pelletier/go-toml/v2"
	"github.com/spf13/afero"
	"github.com/spf13/cast"
	yaml "gopkg.in/yaml.v2"
)

// Decoder provides some configuration options for the decoders.
type Decoder struct {
	// Delimiter is the field delimiter used in the CSV decoder. It defaults to ','.
	Delimiter rune

	// Comment, if not 0, is the comment character ued in the CSV decoder. Lines beginning with the
	// Comment character without preceding whitespace are ignored.
	Comment rune
}

// OptionsKey is used in cache keys.
func (d Decoder) OptionsKey() string {
	var sb strings.Builder
    
func (d Decoder) UnmarshalTo(data []byte, f Format, v any) error {
	var err error

	switch f {
	case JSON:
		err = json.Unmarshal(data, v)
	case XML:
		var xmlRoot xml.Map
		xmlRoot, err = xml.NewMapXml(data)

		var xmlValue map[string]any
		if err == nil {
			xmlRootName, err := xmlRoot.Root()
			if err != nil {
				return err
			}
			xmlValue = xmlRoot[xmlRootName].(map[string]any)
		}

		switch v := v.(type) {
		case *map[string]any:
			*v = xmlValue
		case *any:
			*v = xmlValue
		}
	case TOML:
		err = toml.Unmarshal(data, v)
	case YAML:
		err = yaml.Unmarshal(data, v)
		if err != nil {
			return err
		}

		// To support boolean keys, the YAML package unmarshals maps to
		// map[interface{}]interface{}. Here we recurse through the result
		// and change all maps to map[string]interface{} like we would've
		// gotten from `json`.
		var ptr any
		switch i := v.(type) {
		case *map[string]any:
			ptr = *i
		case *any:
			ptr = *i
		default:
			// Not a map.
		}

		if ptr != nil {
			if mm, changed := stringifyMapKeys(ptr); changed {
				switch i := v.(type) {
				case *map[string]any:
					*i = mm.(map[string]any)
				case *any:
					*i = mm
				}
			}
		}
	case CSV:
		return d.unmarshalCSV(data, v)

	default:
		return fmt.Errorf("unmarshal of format %q is not supported", f)
	}

	if err == nil {
		return nil
	}

	return fmt.Errorf("unmarshal failed: %w", err)
}