This gist consists of 3 skill responses that together show how to use the new APL back stack extension with a voice command. Page1.json shows a response that renders the first page of the interaction. Note that we load the back extension and set a backstackId on Page1 so it is added to the back stack. When a customer speaks an utterance (say "go…

GoBack.json

//When a customer says "go back" or something similar next a skill 
//can respond with GoBack.json to navigate back on the back stack. 
//Note that the "token" value for the GoBack response's ExecuteCommands 
//directive and the token value for the APL document currently 
//rendered (Page2.json) must be the same. This is how Alexa knows where 
//to direct the commands. 

{
	"outputSpeech": {
		"type": "SSML",
		"ssml": "<speak>Going back!</speak>"
	},
	"directives": [{
        "type": "Alexa.Presentation.APL.ExecuteCommands",
        "token": "MySkill",
        "commands": [{
            "type": "Back:GoBack"
        }]
    }]
}

Page1.json

//Page1.json shows a response that renders the first page of the interaction. 
//Note that we load the back extension and set a backstackId on Page1 so it
//is added to the back stack.

{
    "outputSpeech": {
        "type": "SSML",
        "ssml": "<speak>Page 1</speak>"
    },
    "directives": [
    {
        "type": "Alexa.Presentation.APL.RenderDocument",
        "token": "MySkill",
        "document": {
            "type": "APL",
            "version": "1.4",
            "extensions": [
                {
                    "name": "Back",
                    "uri": "aplext:backstack:10"
                }
            ],
            "settings": {
                "Back": {
                    "backstackId": "Page1"
                }
            },
            "mainTemplate": {
                "items": [
                {
                    "type": "Container",
                    "height": "100%",
                    "width": "100%",
                    "items": [
                    {
                        "type": "Text",
                        "text": "Page 1"
                    },
                    {
                        "type": "AlexaButton",
                        "buttonText": "Go Back",
                        "id": "containedButtonId",
                        "paddingLeft": "@spacingLarge",
                        "paddingRight": "@spacingLarge",
                        "paddingBottom": "@spacingLarge",
                        "paddingTop": "@spacingLarge",
                        "primaryAction": {
                            "type": "Back:GoBack"
                        }
                    },
                    {
                        "type": "Container",
                        "bind": {
                            "name": "Responsible",
                            "value": "${environment.extension.Back.responsibleForBackButton}"
                        },
                        "firstItem": {
                            "type": "Text",
                            "text": "There are ${environment.extension.Back.backstack.length} items on the back stack"
                        },
                        "data": "${environment.extension.Back.backstack}",
                        "items": {
                            "type": "Text",
                            "text": "Backstack ${index}: '${data}'"
                        },
                        "lastItem": {
                            "type": "Text",
                            "text": "The back button ${Responsible ? 'should' : 'should not'} to be drawn"
                        }
                    }
                    ]
                }
                ]
            }
        },
        "datasources": {}
    }
    ]
}

Page2.json

//When a customer speaks an utterance (say "go to page 2") a skill would
//respond with Page2.json. This document again loads the back stack extension 
//and adds itself to the back stack. Now we have 2 APL documents in the back stack.

{
    "outputSpeech": {
        "type": "SSML",
        "ssml": "<speak>Page 2</speak>"
    },
    "directives": [
    {
        "type": "Alexa.Presentation.APL.RenderDocument",
        "token": "MySkill",
        "document": {
            "type": "APL",
            "version": "1.4",
            "extensions": [
                {
                    "name": "Back",
                    "uri": "aplext:backstack:10"
                }
            ],
            "settings": {
                "Back": {
                    "backstackId": "Page2"
                }
            },
            "mainTemplate": {
                "items": [
                    {
                    "type": "Container",
                    "height": "100%",
                    "width": "100%",
                    "items": [
                    {
                        "type": "Text",
                        "text": "Page 2"
                    },
                    {
                        "type": "AlexaButton",
                        "buttonText": "Go Back",
                        "id": "containedButtonId",
                        "paddingLeft": "@spacingLarge",
                        "paddingRight": "@spacingLarge",
                        "paddingBottom": "@spacingLarge",
                        "paddingTop": "@spacingLarge",
                        "primaryAction": {
                            "type": "Back:GoBack"
                        }
                    },
                    {
                        "type": "Container",
                        "bind": {
                            "name": "Responsible",
                            "value": "${environment.extension.Back.responsibleForBackButton}"
                        },
                        "firstItem": {
                            "type": "Text",
                            "text": "There are ${environment.extension.Back.backstack.length} items on the back stack"
                        },
                        "data": "${environment.extension.Back.backstack}",
                        "items": {
                            "type": "Text",
                            "text": "Backstack ${index}: '${data}'"
                        },
                        "lastItem": {
                            "type": "Text",
                            "text": "The back button ${Responsible ? 'should' : 'should not'} to be drawn"
                        }
                    }
                    ]
                }
                ]
            }
        },
        "datasources": {}
    }
    ]
}