APL Document

An APL document is a JSON object that defines a template to display on a device with a screen. The APL document controls the structure and layout. You send the document to the device with the Alexa.Presentation.APL.RenderDocument directive.

Sample APL documents

This example shows an APL document that inflates a single Text component.

{
  "type": "APL",
  "version": "1.5",
  "mainTemplate": {
    "item": {
      "type": "Text",
      "text": "Hello, world"
    }
  }
}

A richer APL document might include imported packages, resource definitions, style definitions, vector graphics, custom layouts, export information, and background colors.

{
  "type": "APL",
  "version": "1.5",
  "description": "A sample APL document",
  "background": "#C87F70",
  "import": [
    {
      "name": "sample-import",
      "source": "https://example.com/packages/fictitious-package-import-example",
      "version": "1.0"
    },
    {
      "name": "alexa-layouts",
      "version": "1.2.0"
    }
  ],
  "export": {
    "resources": [
      "CompanyBlue"
    ],
    "layouts": [
      {
        "name": "myBody",
        "description": "Two stacked text blocks"
      }
    ]
  },
  "resources": [
    {
      "colors": {
        "CompanyBlue": "#0022f3"
      }
    }
  ],
  "styles": {
    "textBlockStyle": {
      "values": [
        {
          "fontSize": 24,
          "color": "@CompanyBlue"
        }
      ]
    }
  },
  "theme": "light",
  "graphics": {
    "AmazonPlayTrailer": {
      "type": "AVG",
      "version": "1.2",
      "parameters": [
        {
          "name": "fillColor",
          "type": "color",
          "default": "black"
        }
      ],
      "width": 48,
      "height": 48,
      "items": {
        "type": "path",
        "pathData": "M24,2C11.869,2,2,11.869,2,24s9.869,22,22,22s22-9.869,22-22S36.131,2,24,2z M24,44C12.972,44,4,35.028,4,24 C4,12.972,12.972,4,24,4s20,8.972,20,20C44,35.028,35.028,44,24,44z M19,34.799V13.201c0-1.004,1.041-1.563,1.829-0.937 l13.53,10.799c0.604,0.479,0.573,1.394-0.031,1.874L20.845,35.736C20.057,36.362,19,35.804,19,34.799z",
        "fillColor": "${fillColor}"
      }
    }
  },
  "layouts": {
    "myBody": {
      "parameters": [
        "block1",
        "block2"
      ],
      "item": {
        "type": "Container",
        "direction": "column",
        "items": [
          {
            "type": "Text",
            "text": "${block1}",
            "style": "textBlockStyle"
          },
          {
            "type": "Text",
            "text": "${block2}",
            "style": "textBlockStyle"
          }
        ]
      }
    }
  },
  "mainTemplate": {
    "parameters": [
      "myDocumentData"
    ],
    "item": {
      "type": "BodyTemplate3",
      "title": "${payload.myTitle}",
      "scrollItem": {
        "type": "myBody",
        "block1": "${myDocumentData.myTextBlock1}",
        "block2": "${myDocumentData.myTextBlock2}"
      }
    }
  }
}

Document properties

An APL document has the following top-level properties.

Property Type Required Description
background Color or Gradient No Override standard background color
commands Map of COMMANDS No Command definitions
description String No An optional description of this document
export Map of exports No An optional list of elements intended to be used by an external package or document.
extensions Array of EXTENSION No An optional list of APL extensions requested by the document
graphics Map of AVG No Vector graphic definitions
handleKeyDown Array of keyboard event handlers No Keyboard event handlers to execute when the user presses a key on the keyboard.
handleKeyUp Array of keyboard event handlers No Keyboard event handlers to execute when the user releases a key on the keyboard.
handleTick Array of tick handlers No Tick handlers to invoke as time passes.
import Array of IMPORTS No A list of references to external APL packages
layouts Map of LAYOUT No Custom layouts
mainTemplate LAYOUT Yes The starting layout
onMount Array of COMMANDS No Command to execute when the document is first displayed
resources RESOURCES No Resource definitions
settings Map of settings No Document-wide settings
styles Map of styles definitions No Style definitions
theme String No Document-specified theme
type "APL" Yes Must be "APL"
version "1.5" Yes Version string of the APL specification. Currently "1.5"

background

The background property is an optional property that initializes the color of the background as the APL document loads. You can set the background property to either a Color or Gradient. Setting the background to a consistent color or gradient keeps the user experience seamless as Alexa switches between different documents.

Because the device parses and interprets the property before loading packages and resources, you can't reference any resources in the background property. The data-binding expressions are limited to the properties in the initial data-binding context. The following are examples of valid background specifications:

"background": "darkgreen"
"background": "rgb(10,255,10)"
"background": {
  "type": "linear",
  "colorRange": [ "darkgreen", "white" ],
  "inputRange": [ 0, 0.25 ],
  "angle": 90
}
"background": "${viewport.theme == 'dark' ? 'darkgreen' : 'lightgreen'}"

When the background property is not specified, the device displays its the default background color. When the background property is partially transparent, the default background color of the device shows through.

commands

The commands property is an object mapping command name to user-defined command definitions.

export

The export property identifies the resources, graphics, layouts, and styles defined in the document that you intend for others to use within documents or packages that import this document as a package. The export property is informational. The APL rendering engine doesn't restrict access to any of the resources, graphics, layouts, or styles defined in a package.

The export property lets you identify which elements you intend to share and which elements are internal to the package and not intended to be directly used. Verification and authoring tools should use export information to help the APL author build a well-structured document.

The export property is a map with the following keys:

Property Type Default Description
graphics Array [] An array of names of graphics
layouts Array [] An array of names of layouts
resources Array [] An array of names of resources
styles Array [] An array of names of styles

Each entry in each of these arrays is an object with the following properties:

Property Type Default Description
name String REQUIRED The name of the element
description String "" An optional description of the exported element

For convenience, you can shorten an entry without a description to a single string containing the name of the entity.

This example shows the export property that includes graphics, layouts, resources, and styles:

{
  "export": {
    "resources": [
      {
        "name": "CompanyRed",
        "description": "Stock color for rendering the company logo"
      },
      {
        "name": "CompanyBlue",
        "description": "For people who don't like red"
      },
      {
        "name": "CompanyGreen" // Description omitted
      },
      "CompanyGray" // May simplify to single string when the description is omitted
    ],
    "layouts": [
      {
        "name": "MediaControl",
        "description": "Media controller with a play and pause button."
      }
    ],
    "graphics": [
      "PlayButton",
      "PauseButton"
    ],
    "styles": [
      "PlayButtonStyle",
      "PauseButtonStyle"
    ]
  }
}

The properties listed in export must be defined in the current document.

extensions

The extensions property lists the APL extensions to request. You can request an extension in both documents and packages. List the requested extensions by name and URI in the extensions property.

This example illustrates requesting three extensions. Note that the "remotebutton" and "fishfeeder" extensions shown here are fictitious.

{
  "extensions": [
    {
      "name": "Back",
      "uri": "aplext:backstack:10"
    },
    {
      "name": "Button",
      "uri": "aplext:remotebutton:13"
    },
    {
      "name": "Fish",
      "uri": "aplext:fishfeeder:10"
    }
  ]
}

Each requested extension is a map with the following keys:

Property Type Default Description
name String REQUIRED The local name/namespace of the extension
uri String REQUIRED The URI of the requested extension

The name property defines how to identify the extension within the APL document. The document uses the name property in three locations:

  1. The names and URIs of all requested and provided extensions are exposed as environment properties. Use this property in your document to determine whether a particular extension is available.
  2. The extension name is used a namespace when writing extension event handlers. This lets the document receive events from the extension and act upon those events.
  3. The extension name is used as a namespace to execute extension commands. This lets the document send a command to the extension.
  4. The extension name is used to retrieve settings from the settings specific to that extension. This lets the extension configure itself at load time, if needed.

For more about how extensions work and how to interact with extensions, see APL Extensions.

The following extensions are available:

graphics

The graphics property defines a collection of named vector graphics you can use within the document. See Alexa Vector Graphics Format for details about the format for vector graphics.

handleKeyDown

An array of keyboard event handlers to execute when a key is pressed on the keyboard or when a key auto-repeats. The keyDown event is generated whenever possible; for example pressing the "shift" key should generate a keyDown event.

The event generated has the form:

"event": {
  "source": {
   "type": "Document",
    "handler": "KeyDown",
    "id": null,        // No value reported
    "uid": null,       // No value reported
    "value": null      // No value reported
  },
  "keyboard": {
    "altKey":   Boolean
    "code":     String,
    "ctrlKey":  Boolean,
    "key":      String,
    "metaKey":  Boolean,
    "repeat":   Boolean,
    "shiftKey": Boolean
  }
}

For more details on the keyboard property, refer to the keyboard events documentation.

handleKeyUp

An array of keyboard event handlers to execute when a key is released on the keyboard. The keyUp event is generated whenver possible and not just for text entry. For example, releasing the "shift" key on a keyboard should generate a keyUp event.

The event generated has the form:

"event": {
  "source": {
   "type": "Document",
    "handler": "KeyUp",
    "id": null,        // No value reported
    "uid": null,       // No value reported
    "value": null      // No value reported
  },
  "keyboard": {
    "altKey":   Boolean
    "code":     String,
    "ctrlKey":  Boolean,
    "key":      String,
    "metaKey":  Boolean,
    "repeat":   Boolean,
    "shiftKey": Boolean
  }
}

For more details on the keyboard property, refer to the keyboard events documentation.

handleTick

An array of tick event handlers to execute as time passes.

The event generated for a tick event handler has the following form.

"event": {
  "source": {
    "type": "Document",
    "handler": "Tick",
    "id": null,       // No value reported
    "uid": null,      // No value reported
    "value": null     // No value reported
  }
}

import

The import property defines a list of named APL packages. You can use the resources, styles, and layouts defined in the imported packages within this document. Specify an array of package references where each entry in the in the list is an object with the following properties.

Property Type Required Description
name String Yes The name of the Package to import
version String Yes The version of the Package to import.
source URL No When provided, a URL from which to download the package.

The following example illustrates importing the alexa-layouts package provided in the Alexa Design System for APL, and an external package provided at a URL.

  "import": [
    {
      "name": "alexa-layouts",
      "version": "1.2.0"
    },
    {
      "name": "my-own-package",
      "source": "https://www.example.com/my-custom-package.json",
      "version": "1.0"
    }	
  ]

Package imports form a directed dependency graph. Resource, style, and layout lookup is depth-first, following the package import order. For example, assume document A depends on packages B and C, and documents B and C depend on the package D. Then the search order for the definition of a resource is A, B, C, and then D. Therefore, package A can override any of the resources, styles, or layouts defined in B, C, or D. Dependency loops are forbidden.

Packages use one of two mechanisms to download.

  • When you provide the source property, the document downloads the package from the specified source URL.
  • When you don't provide the source property, the document retrieves the package from an Alexa-supported central repository of packages, using the package name and version properties. For the current set of Amazon-provided packages, see Alexa Design System for APL.

The device runtime software caches packages. The device considers that two packages are identical if their name and version properties match (even if they have specified different source properties). The time to live (TTL) of a package is determined by the TTL received during download.

As you develop and test a package, assign it a unique pre-release or build tag each time you modify the package. This forces the runtime to reload the new version of the package rather than using the cached version during testing.

When you host your own APL packages on a site such as Amazon S3, be sure to enable Cross-Origin Resource Sharing for any APL resources hosted on an HTTPS endpoint.

name

Package names follow the pattern [a-zA-Z][a-zA-Z0-9-]*.

source

The source property, if specified, provides the URL location from which to download the package. When not specified, the package is retrieved from an Alexa-supported central repository. For the current set of Amazon-provided packages, see Alexa Design System for APL.

Use https instead of http for package source URLs. Many Alexa devices don't support the http scheme in skill APL documents for security reasons.

version

Package versions should follow the semantic versioning convention given by the grammar:

vers         ::= <<release>> <<prerelease>>? <<build>>?
release      ::= <<number>> "." <<number>> "." <<number>>
prerelease   ::= "-" <<identifier>> ( "." <<identifier>> )*
build        ::= "+" <<identifier>> ( "." <<identifier>> )*
identifier   ::= [a-zA-Z0-9-]+
number       ::= [0-9] | [1-9][0-9]+

Examples of valid package versions include: 10.2.1, 0.1.10-beta.3, and 0.9.7-alpha2.17+build.1002.

layouts

The layouts property is a map of layout name to layout definition. See APL Layout.

mainTemplate

The mainTemplate property is the layout that to inflate when the document is first shown on the screen. You send Alexa the RenderDocument) directive to display your document.

The parameters defined in the mainTemplate are bound to data sources provided in the RenderDocument directive that inflated the document.

The mainTemplate is the layout that will be inflated when the document is first shown on the screen. The parameters defined in the mainTemplate will be bound to data sources provided by the RenderDocument directive that initiated the display of the APL document. See RenderDocument.

onMount

The command to execute when this document is first displayed on the screen. This command is executed after the component onMount commands are executed.

When the device first displays the document on the screen, the following sequence of actions takes place:

  1. Execute in parallel all of the component onMount commands.
  2. Execute the document onMount command.

These commands are effectively gathered into the following meta-command:

{
  "type": "Sequential",
  "commands": [
    {
      "type": "Parallel",
      "commands": "<COMPONENT_ON_MOUNT_COMMANDS>"
    }
  ],
  "finally": "<DOCUMENT_ON_MOUNT_COMMAND>"
}

The reason for this structure is because a touch event or an external command could be issued against the document while the component onMount commands are executing. If the event occurs while the component onMount commands are executing, they will be terminated and the document onMount command will be executed in fast mode. If the event occurs while the document onMount command is executing, it will be terminated.

The event generated has the form:

"event": {
  "source": {
    "type": "Document",
    "handler": "Mount",
    "id": null,        // No value reported
    "uid": null,       // No value reported
    "value": null      // No value reported
  }
}

resources

The resources property is an array of resource blocks. See Resources.

settings

The settings property holds a map of key-value pairs that define document-wide properties. The following properties are defined:

Property Type Default Description
idleTimeout Number <system> Time before document closes due to inactivity

For example, to set a two minutes default idle timeout, specify:

{
  "type": "APL",
  "version": "1.5",
  "settings": {
    "idleTimeout": 120000
  }
}

The information contained in the settings property are not accessible through data-binding or elsewhere in the APL document. They only serve to provide configuration information to the process displaying the APL document.

A device or runtime using APL may add custom device- or runtime-specific settings. To avoid conflicts with future global settings properties, it is recommended that the name of any custom device- or runtime-specific settings property starts with a hyphen or an uppercase letter. For example, "-idleTimeoutWhenDark" or "IdleTimeoutWhenDark".

idleTimeout

Recommended time in milliseconds that the document should remain on the screen before closing due to inactivity. This value is a recommendation, not a guarantee. Specific devices may choose to ignore or bound the idle timeout value.

styles

The styles property is an object mapping style name to style definition. See Styles

theme

If specified, the theme value overrides the viewport.theme property in the data-binding context. See Viewport object – Theme.

version

The version property specifies the version of APL that the APL document uses. The version property is used by the APL rendering engine to identify required features and ensure rendering accuracy.

An APL rendering engine should refuse to render a document if it does not support the document's version number. Rendering engines should be backward-compatible. A "1.5" engine also supports "1.4" and earlier documents.

The current version of the APL specification is "1.5". If a document has an older version number such as "1.0", but tries to use newer features from the 1.1 or later specification (such as the AnimateItem command), then the rendering behavior is undefined. The rendering engine is only obligated to render the "1.0" features and might ignore newer features.

To create a document that uses newer features, but still works correctly on devices with older versions of APL, wrap the newer features in a conditional block with the environment.aplVersion property.

{
  "when": "${environment.aplVersion == '1.5'}",
  "type": "VectorGraphic",
  "source": "sample-vector-graphic",
  "position": "absolute",
  "fillColor": "yellow",
  "top": "3vh",
  "left": "3vw"
}

Inflation of An APL document

The APL document is inflated into an on-screen display, using the following steps:

1. Put the list of import packages on the package processing queue.

2. For each package on the queue:

  • Add the package to the directed graph of package dependencies

  • Check if the package is available either in the (a) on-device cache, or (b) the packages portion of the directive. If the package is not on-device, use the source value of the import list to download the package from the named URL.

  • Add the packages import list to the package processing queue

3. Construct an initial data-binding context with a viewport property.

4. Construct an initial set of named resources using the built-in resources for the device.

5. Traversing the directed graph of package dependencies in depth-first order, for each package:

For each resource block in the resources array:

Evaluate the when clause in the current data-binding context. If the when clause evaluates to false, skip this block. Otherwise, if the when clause evaluates to true:

  • Evaluate each boolean in the boolean map and add to the resources

  • Evaluate each color in the colors map and add to the resources

  • Evaluate each number in the numbers map and add to the resources

  • Evaluate each string in the strings map and add to the resources

  • Evaluate each dimension in the dimensions map and add to the resources

6. For each parameter in the mainTemplate:

  • Identify a data source with the same name

  • Update the data-binding context to set that name to the value in the data source.

7. Inflate the mainTemplate following standard layout inflation logic.