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: property.go
    path of file: ./repos/pdfcpu/pkg/pdfcpu/validate
    
    the code of the file until where you have to start completion: /*
Copyright 2018 The pdfcpu Authors.

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
    
func validatePropertiesDict(xRefTable *model.XRefTable, o types.Object) error {
	// see 14.6.2
	// a dictionary containing private information meaningful to the conforming writer creating marked content.
	// anything possible +
	// empty dict ok
	// Optional Metadata entry ok
	// Optional Contents entry ok
	// Optional Resources entry ok
	// Optional content group /OCG see 8.11.2
	// Optional content membership dict. /OCMD see 8.11.2.2
	// Optional MCID integer entry
	// Optional Alt since 1.5 see 14.9.3
	// Optional ActualText since 1.5 see 14.9.4
	// Optional E see since 1.4 14.9.5
	// Optional Lang string RFC 3066 see 14.9.2

	logProp := func(qual, k string, v types.Object) {
		if log.ValidateEnabled() {
			log.Validate.Printf("validatePropertiesDict: %s key=%s val=%v\n", qual, k, v)
		}
	}

	d, err := xRefTable.DereferenceDict(o)
	if err != nil || d == nil {
		return err
	}

	if err = validateMetadata(xRefTable, d, OPTIONAL, model.V14); err != nil {
		return err
	}

	for key, val := range d {

		switch key {

		case "Metadata":
			logProp("known", key, val)

		case "Contents":
			logProp("known", key, val)
			if _, err = validateStreamDict(xRefTable, val); err != nil {
				return err
			}

		case "Resources":
			logProp("known", key, val)
			if _, err = validateResourceDict(xRefTable, val); err != nil {
				return err
			}

		case "OCG":
			logProp("unsupported", key, val)
			return errors.Errorf("validatePropertiesDict: unsupported key \"%s\"\n", key)

		case "OCMD":
			logProp("unsupported", key, val)
			return errors.Errorf("validatePropertiesDict: unsupported key \"%s\"\n", key)

		//case "MCID": -> default
		//case "Alt": -> default
		//case "ActualText": -> default
		//case "E": -> default
		//case "Lang": -> default

		default:
			logProp("unknown", key, val)
			if _, err = xRefTable.Dereference(val); err != nil {
				return err
			}
		}

	}

	return nil
}