index.bs

<h1>Clipboard API and events</h1>

<pre class="metadata">
Shortname: clipboard-apis
Level:
Group: webplatform
Status: ED
TR: https://www.w3.org/TR/clipboard-apis/
ED: https://w3c.github.io/clipboard-apis/
Repository: w3c/clipboard-apis
Editor: Gary Kacmarcik, Google, garykac@google.com
Editor: Grisha Lyukshin, Microsoft, gked@microsoft.com
Editor: Hallvord R. M. Steen, Mozilla - emeritus
Abstract:
	This document describes APIs for clipboard operations such as copy, cut and
    paste in web applications.
</pre>

<pre class="anchors">
urlPrefix: https://html.spec.whatwg.org/multipage/interaction.html#; type: dfn;
	text: drag data store mode
	text: drag data item kind
	text: drag data item type string
	text: concept dnd rw
	text: concept dnd ro
	text: concept dnd p
	text: focusable area
	text: dom anchor
url: https://html.spec.whatwg.org/multipage/dom.html#the-body-element-2; type: dfn;
	text: the body element
urlPrefix: http://www.w3.org/TR/html5/browsers.html#; type: dfn;
	text: allowed to show a popup
urlPrefix: https://dom.spec.whatwg.org/#; type: dfn;
	text: constructing events
urlPrefix: http://w3c.github.io/editing/contentEditable.html#dfn-; type: dfn;
	text: editing host
spec: ecma-262; urlPrefix: http://tc39.github.io/ecma262/
    type: dfn
        text: Assert; url: sec-algorithm-conventions
        text: promise; url: sec-promise-objects
</pre>

<pre class="biblio">
{
	"RFC2392": {
		"title": "Content-ID and Message-ID Uniform Resource Locators. August 1998. Internet RFC 2392.",
		"href": "http://www.ietf.org/rfc/rfc2392.txt",
		"authors": [ "E. Levinson" ]
	},
	"HTMLEA": {
		"title": "HTML Editing APIs",
		"href": "https://dvcs.w3.org/hg/editing/raw-file/tip/editing.html",
		"authors": ["Aryeh Gregor. W3C Editing APIs CG."]
	 },
	"HTMLLS": {
		"title": "HTML Living Standard",
		"href": "https://html.spec.whatwg.org/multipage/",
		"authors": [ "Ian Hickson. WHATWG." ]
	 },
	"MICROSOFT-CLIP-OP": {
		"title": "About DHTML Data Transfer. Microsoft Developer Network.",
		"href": "http://msdn.microsoft.com/en-us/library/ms537658.aspx"
	}
}
</pre>


<h2 id="secintro">Introduction</h2>

	<i>This section is non-normative.</i>

	This specification defines the common clipboard operations of cutting,
	copying and pasting, in such a way that they are exposed to Web Applications
	and can be adapted to provide advanced functionalities. Its goal is to
	provide for compatibility where possible with existing implementations.


<h2 id="Cases">Use Cases</h2>

	<i>This section is non-normative.</i>

	There are many use cases for being able to change the default clipboard
	operations (cut/copy/paste). We have collected
	a few samples to demonstrate possible uses, although these may not all be
	supported by this specification.

	<h3 id="Rich">Rich content editing</h3>

		When copying text which contains hyperlinks or other structure,
		it is often useful to be able to reformat the content to preserve
		important information.

	<h3 id="graphics-semantics">Graphics with built-in semantics</h3>

		In order to make web applications which allow the manipulation of rich
		text, or of graphic content such as [[SVG]], it is useful to provide a
		mechanism that allows for copying more than just the rendered content.

	<h3 id="Mathematic">Mathematical information</h3>

		With content such as mathematics, simply copying rendered text and pasting
		it into another application generally leads to most of the semantics being
		lost. MathML often needs to be transformed to be copied as plain text, for
		example to make sure "to the power of" is shown with the caret  "^" sign
		in a formula plain-text input. The XML source could also be placed in the
		clipboard with the appropriate transformation occurring at paste time.


<h2 id="terminolofy">Terminology</h2>

	The term <dfn>editable context</dfn> means any element that is either an
	[=editing host=], a textarea element, or an input element with its type
	attribute set to any of "text", "search", "tel",
	"url", "email", "password" or "number".


<h2 id="model">Model</h2>

	The platform provides a <dfn>system clipboard</dfn>.

	The [=system clipboard=] has a list of clipboard items that are collectively
	called the <dfn>system clipboard data</dfn>. The [=system clipboard data=] is
	a {{DataTransfer}} object that mirrors the contents of the clipboard.


<h2 id="clipboard-events-and-interfaces">Clipboard Events</h2>

	<h3 id="clipboard-event-interfaces">Clipboard event interfaces</h3>

		The ClipboardEvent interface extends the {{Event}} interface.

		<div id="clipboardeventinit-idl">

		<pre class="idl" data-highlight="webidl">
		dictionary ClipboardEventInit : EventInit {
		  DataTransfer? clipboardData = null;
		};
		</pre>

		: <dfn for="ClipboardEventInit">clipboardData</dfn>
		:: A {{DataTransfer}} object to hold data and meta data related to the event.

		</div>
		<div id="clipboardevent-idl">

		<pre class="idl" data-highlight="webidl">
		[Constructor(DOMString type, optional ClipboardEventInit eventInitDict)]
		interface ClipboardEvent : Event {
		  readonly attribute DataTransfer? clipboardData;
		};
		</pre>

		: <dfn for="ClipboardEvent">clipboardData</dfn>

		:: The clipboardData attribute is an instance of the {{DataTransfer}}
			interface which lets a script read and manipulate values on the system
			clipboard during user-initiated copy, cut and paste operations. The
			associated drag data store is a live but filtered view of the system
			clipboard, exposing [=mandatory data types=] the implementation knows
			the script can safely access. For synthetic events, the drag data store
			contains the data added by the script that created the event.
		:: The clipboardData object's {{DataTransfer/items}} and
			{{DataTransfer/files}} properties enable processing of multi-part or
			non-textual data from the clipboard.

		</div>

		The interface can be used to <a lt="constructing events">construct events</a>.
		An example is given below:

		<pre class="example javascript">
			var pasteEvent = new ClipboardEvent('paste');
			pasteEvent.clipboardData.items.add('My string', 'text/plain');
			document.dispatchEvent(pasteEvent);
		</pre>

		Note: Synthetic clipboard events will not actually modify the clipboard or
		the document. In other words, while the script above will fire a paste event,
		the data will not be pasted into the document.

		<!-- Issue: There should be a way a script can check if a clipboard format
		is registered and whether the implementation allows writing this format to
		the clipboard! event.clipboardData.isTypeSupported('mime/type')</em>?
		-->

	<h3 id="clipboard-event-definitions"><dfn>Clipboard events</dfn></h3>

		<h4 id="clipboard-event-clipboardchange">The <dfn>clipboardchange</dfn> event</h4>

			The [=clipboardchange=] event fires whenever the contents of the
			[=system clipboard=] are changed. These changes could be due to any of the
			following (non-exhaustive):
			
			* User-initiated cut or copy actions
			* Scripts that use the [[#async-clipboard-api]] to write to the clipboard
			* Actions that update the clipboard outside the user agent

			If the clipboard contents are changed outside the user agent, then the
			[=clipboardchange=] event MUST fire when the user agent regains focus.
			
			Since synthetic [=cut=] and [=copy=] events do not update the [=system clipboard=],
			they will not trigger a "clipboardchange" event.

		<h4 id="clipboard-event-copy">The <dfn>copy</dfn> event</h4>

			When the user initiates a copy action, the user agent
			[=fire a clipboard event|fires a clipboard event=] named
			[=copy=].
			
			If the event is not canceled, the currently selected
			data will be copied to the [=system clipboard=].
			The current document selection is not affected.

			The [=copy=] event bubbles and is cancelable.
			
			See [[#copy-action]] for a detailed description of the processing model for
			this event.
			
			A synthetic [=copy=] event can be manually constructed and dispatched, but it
			will not affect the contents of the [=system clipboard=].

		<h4 id="clipboard-event-cut">The <dfn>cut</dfn> event</h4>

			When the user initiates a cut action, the user agent
			[=fire a clipboard event|fires a clipboard event=] named
			[=cut=].
			
			In an [=editable context=], if the event is not
			canceled the action will place the currently selected data on the
			[=system clipboard=] and remove the selection from the document.
			The [=cut=] event fires before the selected data is removed. When
			the cut operation is completed, the selection is collapsed.

			In a non-[=editable context=], the {{ClipboardEvent/clipboardData}} will
			be an empty list. Note that the [=cut=] event will still be fired
			in this case.

			The [=cut=] event bubbles and is cancelable.

			See [[#cut-action]] for a detailed description of the processing model for
			this event.
			
			A synthetic [=cut=] event can be manually constructed and dispatched, but it
			will not affect the contents of the document or of the [=system clipboard=].

		<h4 id="clipboard-event-paste">The <dfn>paste</dfn> event</h4>

			When a user initiates a paste action, the user agent
			[=fire a clipboard event|fires a clipboard event=] named
			[=paste=]. The event fires before any clipboard data is inserted
			into the document.

			If the cursor is in an [=editable context=], the paste action will
			insert clipboard data in the most suitable format (if any) supported
			for the given context.

			The paste action has no effect in a non-[=editable context=],
			but the [=paste=] event fires regardless.

			The [=paste=] event bubbles and is cancelable.

			See [[#paste-action]] for a detailed description of the processing model for
			this event.
			
			A synthetic [=paste=] event can be manually constructed and dispatched, but it
			will not affect the contents of the document.

	<h3 id="integration-with-other-scripts-and-events">Integration with other scripts and events</h3>

		<h4 id="allow-modify-clipboard">Event handlers that are <dfn>allowed to modify the clipboard</dfn></h4>

			Event handlers may write to the clipboard if any of the following is
			true:

			* The action which triggers the event is invoked from the user-agent's
				own user interface, e.g. from a "Copy" menu entry or shortcut key.
			* The action which triggers the event is invoked from a scripting thread
				which is [=allowed to show a popup=].

			The implementation <em>may</em> allow other trusted event types to
			modify the clipboard if the implementation authors believe that those
			event types are likely to express user intention. The implementation
			<em>may</em> also support configuration that trusts specific sites or
			apps to modify the clipboard regardless of the origin of the scripting
			thread.

			Synthetic [=cut=] and [=copy=] events <em>must not</em> modify data on the
			system clipboard.

		<h4 id="allow-read-clipboard">Event handlers that are <dfn>allowed to read from clipboard</dfn></h4>

			Event handlers may read data from the system clipboard if either of the
			following is true

			* The action that triggers the event is invoked from the user-agent's
				own user interface, e.g. a "Paste" menu entry or shortcut key.
			* The script that triggers the action is running on a site which through
				an implementation-dependant mechanism is given permission to read
				data from the clipboard.
			* The action that triggers the event is triggered in an app with
				permissions to read the clipboard.

			Synthetic [=paste=] events <em>must not</em> give a script access to data on
			the real system clipboard.

		<h4 id="integration-with-rich-text-editing">Integration with rich text editing APIs</h4>

			If an implementation supports ways to execute clipboard commands through
			scripting, for example by calling the
			<code>document.execCommand()</code> method with the commands "cut",
			"copy" and "paste", the implementation <em>must</em> trigger the
			corresponding action, which again will dispatch the associated clipboard
			event.

			These are the steps to follow when triggering copy, cut or paste actions
			through a scripting API:

			1. Execute the corresponding action synchronously.
			1. Use the action's return value as the return value for the API call.

			Note: Copy and cut commands triggered through a scripting API will only
			affect the contents of the real clipboard if the event is dispatched
			from an event that is trusted and triggered by the user, or if the
			implementation is configured to allow this. Paste commands triggered
			through a scripting API will only fire paste events and give access to
			clipboard contents if the implementation is configured to allow this.
			How implementations can be configured to allow read or write access to
			the clipboard is outside the scope of this specification.

		<h4 id="otherevents">Interaction with other events</h4>

			If the clipboard operation is triggered by keyboard input, the
			implementation <em>must</em> fire the corresponding event that initiates
			the clipboard operation. The event is asynchronous but <em>must</em> be
			dispatched before <b>keyup</b> events for the relevant keys.

			The cut and paste actions <em>may</em> cause the implementation to
			dispatch other supported events, such as textInput, input, change,
			validation events, DOMCharacterDataModified and DOMNodeRemoved /
			DOMNodeInserted. Any such events are queued up to fire after processing
			of the cut/paste event is finished.

			The implementation <em>must not</em> dispatch other input-related events
			like textInput, input, change, and validation events in response to the
			copy operation.

		<h4 id="selection-mod">Event listeners that modify selection or focus</h4>

			If the event listener modifies the selection or [=focusable area=], the clipboard
			action <em>must</em> be completed on the modified selection.

<h2 id="sync-clipboard-api">Synchronous Clipboard API</h2>

	The Synchronous Clipboard API allows you to override the default cut, copy
	and paste behavior of the user agent.

	Synchronous access to the clipboard is performed using the standard
	{{DataTransfer}} methods to mutate the {{DataTransfer/items}} on a
	{{ClipboardEvent}}'s {{ClipboardEvent/clipboardData}} attribute.
	One consequence of this is that the synchronous clipboard APIs can only
	access clipboard data in the context of a {{ClipboardEvent}} handler.

	Note: If you need to access the clipboard outside of a clipboard event
	handler, see [[#async-clipboard-api]].

	<h3 id="override-copy">Overriding the copy event</h3>

		To override the default [=copy=] event behavior, a [=copy=] event
		handler must be added and this event handler must call
		{{Event/preventDefault()}} to cancel the event.
		
		Canceling the event is required in order for the [=system clipboard=] to be
		updated with the data in {{ClipboardEvent/clipboardData}}.
		If the {{ClipboardEvent}} is not canceled, then the data from the
		current document selection will be copied instead.

		<pre class="example javascript">
		// Overwrite what is being copied to the clipboard.
		document.addEventListener('copy', function(e) {
			// e.clipboardData is initially empty, but we can set it to the
			// data that we want copied onto the clipboard.
			e.clipboardData.setData('text/plain', 'Hello, world!');
			e.clipboardData.setData('text/html', '&lt;b&gt;Hello, world!&lt;/b&gt;');

			// This is necessary to prevent the current document selection from
			// being written to the clipboard.
			e.preventDefault();
		});
		</pre>

	<h3 id="override-cut">Overriding the cut event</h3>

		To override the default [=cut=] event behavior, a [=cut=] event
		handler must be added and this event handler must call
		{{Event/preventDefault()}} to cancel the event.
		
		Canceling the event is required in order for the [=system clipboard=] to be
		updated with the data in {{ClipboardEvent/clipboardData}}.
		If the {{ClipboardEvent}} is not canceled, then the data from the
		current document selection will be copied instead.

		Note that canceling the [=cut=] event will also prevent the document from
		being updated (i.e., the current selection will not be removed). The event
		handler will need to manually update the document to remove the currently
		selected text.
		
		<pre class="example javascript">
		// Overwrite what is copied to the clipboard.
		document.addEventListener('cut', function(e) {
			// e.clipboardData is initially empty, but we can set it to the
			// data that we want copied onto the clipboard as part of the cut.
			// Write the data that we want copied onto the clipboard.
			e.clipboardData.setData('text/plain', 'Hello, world!');
			e.clipboardData.setData('text/html', '&lt;b&gt;Hello, world!&lt;/b&gt;');

			// Since we will be canceling the cut operation, we need to manually
			// update the document to remove the currently selected text.
			deleteCurrentDocumentSelection();

			// This is necessary to prevent the document selection from being
			// written to the clipboard.
			e.preventDefault();
		});
		</pre>

	<h3 id="override-paste">Overriding the paste event</h3>

		To override the default [=paste=] event behavior, a [=paste=] event
		handler must be added and this event handler must call
		{{Event/preventDefault()}} to cancel the event.
		
		Canceling the event is required so that the user agent does not update the
		document with data from the [=system clipboard=].

		Note that canceling the [=paste=] event will also prevent the document from
		being updated (i.e., nothing will be pasted into the document). The event
		handler will need to manually paste the data into the document.
		
		Also note that, when pasting, the [=drag data store mode=] flag is
		<a lt="concept dnd ro">read/only</a>, hence calling {{DataTransfer/setData()}} from a
		[=paste=] event handler will not modify the data that is
		inserted, and not modify the data on the clipboard.

		<pre class="example javascript">
		// Overwrite what is being pasted onto the clipboard.
		document.addEventListener('paste', function(e) {
			// e.clipboardData contains the data that is about to be pasted.
			if (e.clipboardData.types.indexOf('text/html') > -1) {
				var oldData = e.clipboardData.getData('text/html');
				var newData = '&lt;b&gt;Ha Ha!&lt;/b&gt; ' + oldData;

				// Since we are canceling the paste operation, we need to manually
				// paste the data into the document.
				pasteClipboardData(newData);

				// This is necessary to prevent the default paste action.
				e.preventDefault();
			}
		});
		</pre>



<h2 id="async-clipboard-api">Asynchronous Clipboard API</h2>

	<h3 id="navigator-interface">Navigator Interface</h3>

		<pre class="idl" data-highlight="webidl">
		partial interface Navigator {
		  [SecureContext SameObject] readonly attribute Clipboard clipboard;
		};
		</pre>

		<div id="navigator-idl" dfn-for="Navigator">

		<div class="algorithm" data-algorithm="navigator-clipboard">
		<h4 id="h-navigator-clipboard"><dfn>clipboard</dfn></h4>
		The [=clipboard=] attribute must return the {{Navigator}}'s [=clipboard=] object.
		</div>

		</div><!-- dfn-for Navigator -->

	<h3 id="clipboard-interface">Clipboard Interface</h3>

		<pre class="idl" data-highlight="webidl">
		[SecureContext] interface Clipboard : EventTarget {
		  Promise&lt;DataTransfer> read();
		  Promise&lt;DOMString> readText();
		  Promise&lt;void> write(DataTransfer data);
		  Promise&lt;void> writeText(DOMString data);
		};
		</pre>

		<div id="clipboard-idl" dfn-for="Clipboard">

		<div class="algorithm" data-algorithm="clipboard-read">
		<h4 id="h-clipboard-read"><dfn>read()</dfn></h4>
		The [=read()=] method must run these steps:

			1. Let |p| be a new [=Promise=].

			1. TODO: Handle access permissions. Reject promise if not allowed.

			1. Run the following steps [=in parallel=]:

				1. Let |data| be a copy of the [=system clipboard data=].

				1. Resolve |p| with |data|.

			1. Return |p|.

			<div></div>

			<pre class="example javascript">
				navigator.clipboard.read().then(function(data) {
					for (var i = 0; i < data.items.length; i++) {
						if (data.items[i].type == "text/plain") {
							console.log(“Your string: ”, data.items[i].getAs(“text/plain”));
						} else {
							console.error(“No text/plain data on clipboard.”);
						}
					}
				});
			</pre>

		</div><!-- read() -->

		<div class="algorithm" data-algorithm="clipboard-readtext">
		<h4 id="h-clipboard-readtext"><dfn>readText()</dfn></h4>
		The [=readText()=] method must run these steps:

			1. Let |p| be a new [=Promise=].

			1. TODO: Handle access permissions. Reject promise if not allowed.

			1. Run the following steps [=in parallel=]:

				1. Let |data| be a copy of the [=system clipboard data=].
				
				1. Let |textData| be an empty string.
				
				1. If |data|'s {{DataTransfer/items}} list contains a "text/plain" item |textItem|, then:
				
					1. Set |textData| to be a copy of |textItem|'s string data

				1. Resolve |p| with |textData|.

			1. Return |p|.

			<div></div>

			<pre class="example javascript">
				navigator.clipboard.read().then(function(data) {
					console.log(“Your string: ”, data);
				});
			</pre>

		</div><!-- readText() -->

		<div class="algorithm" data-algorithm="clipboard-write">
		<h4 id="h-clipboard-write-data"><dfn>write(|data|)</dfn></h4>
		The [=write(data)=] method must run these steps:

			1. Let |p| be a new [=Promise=].

			1. TODO: Handle access permissions. Reject promise if not allowed.

			1. Run the following steps [=in parallel=]:

				1. Let |cleanItemList| be an empty {{DataTransferItemList}}.

				1. For each {{DataTransferItem}} |item| in |data|'s {{DataTransfer/items}} list:

					1. Let |cleanItem| be a sanitized copy of |item|.

					1. If unable to create a sanitized copy, then reject |p|.

					1. Add |cleanItem| to |cleanItemList|.

				1. Replace the [=system clipboard data=]'s {{DataTransfer/items}}
					list with |cleanItemList|.

				1. Resolve |p|.

			1. Return |p|.

			<div></div>

			<pre class="example javascript">
				var data = new DataTransfer();
				data.items.add("text/plain", "Howdy, partner!");
				navigator.clipboard.write(data).then(function() {
					console.log(“Copied to clipboard successfully!”);
				}, function() {
					console.error(“Unable to write to clipboard. :-(”);
				});
			</pre>

		</div><!-- write() -->

		<div class="algorithm" data-algorithm="clipboard-writetext">
		<h4 id="h-clipboard-writetext-data"><dfn>writeText(|data|)</dfn></h4>
		The [=writeText(data)=] method must run these steps:

			1. Let |p| be a new [=Promise=].

			1. TODO: Handle access permissions. Reject promise if not allowed.

			1. Run the following steps [=in parallel=]:

				1. Let |newItemList| be an empty {{DataTransferItemList}}.

				1. Let |newItem| be a new {{DataTransferItem}} with
					[=drag data item kind=] set to <em>string</em> and
					[=drag data item type string=] set to <em>text/plain</em>.
					
				1. Set |newItem|'s data to |data|.

				1. Add |newItem| to |newItemList|.

				1. Replace the [=system clipboard data=]'s {{DataTransfer/items}}
					list with |newItemList|.

				1. Resolve |p|.

			1. Return |p|.

			<div></div>

			<pre class="example javascript">
				navigator.clipboard.writeText("Howdy, partner!").then(function() {
					console.log(“Copied to clipboard successfully!”);
				}, function() {
					console.error(“Unable to write to clipboard. :-(”);
				});
			</pre>

		</div><!-- writeText() -->
		
		</div><!-- dfn-for Clipboard -->


<h2 id="clipboard-actions">Clipboard Actions</h2>

	This section defines clipboard actions and the processing model
	for event dispatch.

	Each clipboard action has two flags called <em>script-triggered</em> and
	<em>script-may-access-clipboard</em>.

	The <dfn>script-triggered</dfn> flag is set if the action runs because
	of a script, for example a <code>document.execCommand()</code> call.
	Future scripting APIs that interact with the clipboard should also use
	these actions, and the <em>script-triggered</em> flag must be set
	accordingly.

	<div class="algorithm" data-algorithm="script-may-access-clipboard">

	The <dfn>script-may-access-clipboard</dfn> flag is set as follows:

	1. If action is <em>copy</em> or <em>cut</em> and the script thread
		is [=allowed to modify the clipboard=], then

		1. Set the action's <em>script-may-access-clipboard</em> flag

	1. If action is <em>paste</em> and the script thread is [=allowed to
		read from clipboard=], then

		1. Set the action's <em>script-may-access-clipboard</em> flag.

	</div><!-- algorithm -->

	<h3 id="copy-action">The copy action</h3>

		<div class="algorithm" data-algorithm="clipboard-copy-action">

		The copy action consists of the following steps:

		1. If the <em>script-triggered</em> flag is set, then

			1. If the <em>script-may-access-clipboard</em> flag is unset, then

				1. Return false from the copy action, terminate this algorithm

		1. [=Fire a clipboard event=] named [=copy=]

		1. If the event was not canceled, then

			1. Copy the selected contents, if any, to the clipboard.
				Implementations <em>should</em> create alternate text/html and
				text/plain clipboard formats when content in a web page is selected.

			1. [=Fire a clipboard event=] named [=clipboardchange=]

		1. Else, if the event was canceled, then

			1. Call the [=write content to the clipboard=] algorithm,
				passing on the {{DataTransferItemList}} list <em>items</em>,
				a <em>clear-was-called</em> flag and a <em>types-to-clear</em>
				list.

		1. Return true from the copy action

		</div><!-- algorithm -->

	<h3 id="cut-action">The cut action</h3>

		<div class="algorithm" data-algorithm="clipboard-cut-action">

		The cut action consists of the following steps:

		1. If the <em>script-triggered</em> flag is set, then

			1. If the <em>script-may-access-clipboard</em> flag is unset, then

				1. Return false from the cut action, terminate this algorithm

		1. [=Fire a clipboard event=] named [=cut=]

		1. If the event was not canceled, then

			1. If there is a selection in an [=editable context=] where
				cutting is enabled, then

				1. Copy the selected contents, if any, to the clipboard.
					Implementations <em>should</em> create alternate
					text/html and text/plain clipboard formats when content
					in a web page is selected.

				1. Remove the contents of the selection from the document
					and collapse the selection.

				1. [=Fire a clipboard event=] named [=clipboardchange=]

				1. Queue tasks to fire any events that should fire due to the
					modification, see
					[[#integration-with-other-scripts-and-events]]
					for details.

			1. Else, if there is no selection or the context is not editable, then

				1. Return false

		1. Else, if the event was canceled, then

			1. Call the [=write content to the clipboard=] algorithm,
				passing on the {{DataTransferItemList}} list <em>items</em>,
				a <em>clear-was-called</em> flag and a <em>types-to-clear</em>
				list.

			1. [=Fire a clipboard event=] named [=clipboardchange=]

		1. Return true from the cut action

		</div><!-- algorithm -->

	<h3 id="paste-action">The paste action</h3>

		For the paste action, the <em>script-may-access-clipboard</em> flag
		depends on an implementation-specific permission mechanism for
		determining what sites or apps may read from the clipboard. When a
		paste action is triggered by a script, the implementation must not
		make clipboard contents available without the user's permission. If
		the permission has not already been granted, the permission prompt
		must include the hostname of the document associated with the script
		thread.

		<div class="algorithm" data-algorithm="clipboard-paste-action">

		The paste action consists of the following steps:

		1. If the <em>script-triggered</em> flag is set, then

			1. If <em>script-may-access-clipboard</em> is unset, then

				1. Return false from the paste action, terminate this algorithm

		1. <a href="#fire-a-clipboard-event">Fire a clipboard event</a>
			named [=paste=]

		1. If the event was not canceled, then

			1. If there is a selection or cursor in an [=editable context=]
				where pasting is enabled, then

				1. Insert the most suitable content found on the clipboard,
					if any, into the context.

				1. Queue tasks to fire any events that should fire due to
					the modification, see
					[[#integration-with-other-scripts-and-events]] for details.

			1. Else

				1. Return false

		1. Else, if the event was canceled

			1. Return false

		1. Return true from the action

		</div><!-- algorithm -->


<h2 id="mandatory-data-types-x"><dfn>Mandatory data types</dfn></h2>

	The implementation must recognise the native OS clipboard format description
	for the following data types, to be able to populate the
	{{DataTransferItemList}} with the correct description for paste events, and
	set the correct data format on the OS clipboard in response to copy and cut
	events.

	<h3 id="reading-from-clipboard">Reading from the clipboard</h3>

		These data types must be exposed by <em>paste</em> events if a
		corresponding native type exists on the clipboard:

		* text/plain
		* text/uri-list
		* text/csv
		* text/css
		* text/html
		* application/xhtml+xml
		* image/png
		* image/jpg, image/jpeg
		* image/gif
		* image/svg+xml
		* application/xml, text/xml
		* application/javascript
		* application/json
		* application/octet-stream

	<h3 id="writing-to-clipboard">Writing to the clipboard</h3>

		These data types must be placed on the clipboard with a corresponding
		native type description if added to a {{DataTransfer}} object during
		<em>copy</em> and <em>cut</em> events.

		* text/plain
		* text/uri-list
		* text/csv
		* text/html
		* image/svg+xml
		* application/xml, text/xml
		* application/json

		Advisement: Warning! The data types that untrusted scripts are allowed to write to the
		clipboard are limited as a security precaution. Untrusted scripts can
		attempt to exploit security vulnerabilities in local software by placing
		data known to trigger those vulnerabilities on the clipboard.


<h2 id="security">Security Considerations</h2>

	Enabling authors to change what is copied by a user, or to make an automated
	copy of something that was never selected and allowing unrestricted calls to
	paste information can raise various security and privacy concerns.

	An example scenario of a problem is where a user selects a link and copies
	it, but a different link is copied to the clipboard. The effect of this can
	range from an unexpected result on pasting to an attempted "phishing" attack.

	<h3 id="pasting-html">Pasting HTML and multi-part data</h3>

		<em>This section is non-normative.</em>

		There are certain security risks associated with pasting formatted or
		multi-part data.

		* The user might paste hidden data without realising is there. This may
			happen if, for example, the markup includes
			&lt;input type="hidden"&gt; tags or HTML comments. Such hidden data
			might contain sensitive information.
		* The user might paste malicious JavaScript into a trusted page.
		* The implementation might grant scripts access to local files the user
			did not intend to expose.

		To determine what policies to use, the factors we consider are:

		* The origin of the data being pasted
		* The origin of data sub-parts such as referenced images
		* The origin of the running script

		This is an overview of the scenarios and the possible security policies:

		<table class="simple">
			<tr>
				<th>Origin of data</th>
				<th>Origin of script</th>
				<th>Rules</th>
			</tr>
			<tr>
				<td rowspan="2">Originates from online source</td>
				<td>Same as data</td>
				<td>Do not sanitize HTML. Do not access any local files.</td>
			</tr>
			<tr>
				<!-- cell span from previous row -->
				<td>Different origin</td>
				<td>Optionally sanitize content. Do not access any local files.</td>
			</tr>
			<tr>
				<td>Originates from local application</td>
				<td>Any</td>
				<td>Do not sanitize HTML. Grant access to local files</td>
			</tr>
		</table>

		Some implementations mitigate the risks associated with pasting rich
		text by stripping potentially malicious content such as SCRIPT elements
		and javascript: links by default when pasting rich text, but allow a
		paste event handler to retrieve and process  the original, un-sanitized
		data.

	<h3 id="general-security-policies">General security policies</h3>

		The implementation <em>must not</em> download referenced online
		resources, or expose their contents in the {{DataTransfer/files}} list
		or {{DataTransferItemList}}.

		If the data on the clipboard is not from a local application, the
		implementation <em>must not</em> give access to any referenced local
		files. For example, if the data contains
		&lt;img src="file://localhost/example.jpg"&gt;
		but the data's origin is an online resource, the implementation must not
		add an entry for example.jpg to the clipboardData.items list.

	<h3 id="nuisances">Nuisance considerations</h3>

		Scripts may use the {{DataTransfer}} API to annoy and confuse users by
		altering the data on the system clipboard from copy and cut events. This
		specification does not attempt to prevent such nuisances, though
		implementations may add additional restrictions.

		Implementations must handle scripts that try to place excessive amounts
		of data on the clipboard gracefully.


<h2 id="privacy">Privacy Considerations</h2>

	Untrusted scripts should not get uncontrolled access to a user's
	clipboard data. This specification assumes that granting access to the
	current clipboard data when a user explicitly initiates a paste
	operation from the user agent's trusted chrome is acceptable. However,
	implementors must proceed carefully, and as a minimum implement the
	precautions below:

	* Objects implementing the {{DataTransfer}} interface to return
		clipboard data <em>must not</em> be available outside the
		ClipboardEvent event handler.
	* If a script stores a reference to an object implementing the
		{{DataTransfer}} interface to use from outside the ClipboardEvent
		event handler, all methods <em>must</em> be no-ops when called
		outside the expected context.
	* Implementations <em>must not</em> let scripts create synthetic
		clipboard events to get access to real clipboard data except if
		configured to do so.
	* Implementations <em>should not</em> let scripts call
		document.execCommand("paste") unless the user has explicitly allowed
		it.

	Implementations may choose to further limit the functionality provided
	by the {{DataTransfer}} interface. For example, an implementation may
	allow the user to disable this API, or configure which web sites should
	be granted access to it.


<h2 id="acknowledge">Acknowledgements</h2>

	<em>This section is informative</em>

	The editors would like to acknowledge the contributions of the former
	editors who helped shepherd this specification through various
	meetings and mailing-list discussions to bring it to its current state.

	* Hallvord R. M. Steen

	The editors would also like to acknowledge their intellectual debt to the
	documentation of Data Transfer functionalities from Microsoft
	[[MICROSOFT-CLIP-OP]] and earlier drafts of the [[HTML5]] specification.
	We are also grateful for the draft "safe copy and paste" from Paul Libbrecht
	(this draft is no longer available on the Web).

	And finally, we would like to acknowledge the contributions made by the following:

	Adam Barth,
	Shawn Carnell,
	Daniel Cheng,
	Daniel Dardailler,
	Al Gilman,
	James Graham,
	James Greene,
	Ian Hickson,
	Lachlan Hunt,
	Philip Jägenstedt,
	Anne van Kesteren,
	Aaron Leventhal,
	Jim Ley,
	Paul Libbrecht,
	"Martijn",
	Glenn Maynard,
	Chris Mills,
	ms2ger,
	Ryosuke Niwa,
	Robert O'Callahan,
	Dave Poehlman,
	"ROBO Design",
	Janina Sajka,
	Rich Schwerdtfeger,
	Jonas Sicking,
	Maciej Stachowiak,
	Mihai Sucan,
	Dmitry Titov,
	Ojan Vafai,
	Tarquin Wilton-Jones,
	Tom Wlodkowski,
	and Boris Zbarsky.


<h2 id="algorithms">Appendix A: Algorithms</h2>

	<div class="algorithm" data-algorithm="write-content-to-clipboard">
	<h3 id="to-write-content-to-clipboard"><dfn>write content to the clipboard</dfn></h3>

		: Input
		:: |items|, a {{DataTransferItemList}} list of items to write
		:: |clear-was-called|, a boolean
		:: |types-to-clear|, a list

		: Output
		:: None

		1. If the |items| list is not empty, then

			1. Clear the clipboard

			1. For each part in the list,

				1. If data type is <i>text/plain</i>, then

					1. Ensure encoding is correct per OS and locale conventions

					1. Normalize line endings according to platform conventions

					1. Place text on clipboard with the appropriate OS clipboard
						format description

				1. Else, if data is of a type listed in the
					[=mandatory data types=] list, then

					1. Place part on clipboard with the appropriate OS clipboard
						format description

				1. Else

					1. This is left to the implementation...

						Issue: It's not good to leave things up to the
						implementation. What should happen here?

						Note: Due to limitations in the implementation of operating
						system clipboards, scripts should not assume that custom
						formats will be available to other applications on the
						system. For example, there is a limit to how many custom
						clipboard formats can be registered in Microsoft Windows.
						While it is possible to use any string for
						<a>setData()</a>'s type argument, sticking to the
						[=mandatory data types=] is strongly recommended.

		1. Else, the |items| list is empty. Follow these steps to determine
			whether to clear the clipboard:

			1. If the list of items is empty and the |clear-was-called|
				flag is <i>true</i>, then

				1. If the |types-to-clear| list is empty, then

					1. Clear the clipboard

				1. Else

					1. Remove types in the |types-to-clear| list from the
						clipboard in an operating system and implementation-specific
						way

						Issue: The "remove specific types from clipboard" feature is
						at risk. It doesn't seem all that important, and it's
						unclear if it can be implemented easily across relevant
						platforms.

	</div><!-- algorithm -->

	<div class="algorithm" data-algorithm="algo-fire-a-clipboard-event">
	<h3 id="to-fire-a-clipboard-event"><dfn>fire a clipboard event</dfn></h3>

		: Input
		:: |e|, the {{ClipboardEvent}} to fire

		: Output
		:: None

		1. Let |clear-was-called| be <em>false</em>

		1. Let |types-to-clear| be an empty list

		1. Let |clipboard-event-data| be a new {{DataTransfer}} object with an empty
			{{DataTransfer/items}} list.

		1. Let |clipboard-entry| be the sequence number of the current
			clipboard content, or null if the OS clipboard does not support
			sequence numbers

		1. Let |trusted| be <em>true</em> if the event is generated by the
			user agent, <em>false</em> otherwise

		1. Let |target| be set as follows:

			1. If the context is editable, then

				1. Set |target| to be the element that contains the
					start of the selection in document order, or
					[=the body element=] if there is no selection or cursor.

			1. Else, if the context is not editable, then

				1. Set |target| to be the [=DOM anchor=] of the [=focusable area=], or
					[=the body element=] if no node has focus.

		1. Process the event as follows:

			1. If |e| is "paste", then

				1. Set the |clipboard-event-data|'s
					internal [=drag data store mode=] flag to
					<a lt="concept dnd rw">read/write</a>.

				1. If |trusted| is <em>true</em>, or the
					implementation is configured to give script-generated events
					read access to the OS clipboard

					1. For each |clipboard-part| on the OS clipboard, carry out these steps:

						1. If |clipboard-part| contains plain text, then

							1. Ensure the text is in the encoding the
								scripting engine uses internally

							1. Let |new-data| be a new {{DataTransferItem}} with
								[=drag data item kind=] set to <em>string</em> and
								[=drag data item type string=] set to <em>text/plain</em>.

							1. Set |new-data|'s data to the plain text.

							1. Add |new-data| to |clipboard-event-data|'s {{DataTransfer/items}}

						1. If |clipboard-part| represents file
							references, then for each file reference:

							1. Determine MIME type of referenced file

							1. Let |new-data| be a new {{DataTransferItem}} with
								[=drag data item kind=] set to <em>file</em> and
								[=drag data item type string=] set to the
								corresponding MIME type, or
								<code>application/octet-stream</code> if the
								file's type is unknown.

							1. Set |new-data|'s data to the file reference data.
							
							1. Add |new-data| to |clipboard-event-data|'s {{DataTransfer/items}}

						1. If |clipboard-part| contains HTML- or
							XHTML-formatted text, according to the operating
							system's convention for describing such clipboard
							formats, then

							1. If the implementation supports pasting HTML, then
								the implementation <em>must</em> process the
								markup by calling [=process an html paste event=]
								with |clipboard-part| and |clipboard-event-data|.

						1. If |clipboard-part| contains data in
							another supported binary or text-based format (see
							[=mandatory data types=]), then

							1. Determine the MIME type of the data

							1. Let |new-data| be a new {{DataTransferItem}}
								with [=drag data item kind=] set to
								<em>file</em>, [=drag data item type string=]
								set to the corresponding MIME type
							
							1. Set |new-data|'s data to be the binary or text-based data.

							1. Add |new-data| to |clipboard-event-data|'s {{DataTransfer/items}}

				1. Update |clipboard-event-data|'s {{DataTransfer/files}} property to match
					entries in |clipboard-event-data|'s {{DataTransfer/items}}.

				1. Update |clipboard-event-data|'s {{DataTransfer/types}} property to match
					entries in |clipboard-event-data|'s {{DataTransfer/items}}.

			1. If |e| is "copy" or "cut", then

				1. Set the associated {{DataTransfer}} object's internal
					[=drag data store mode=] flag to <a lt="concept dnd rw">read/write</a>

		1. Set |e|'s {{ClipboardEvent/clipboardData}} to |clipboard-event-data|.

		1. Set |e|'s {{Event/isTrusted}} to |trusted|.

		1. Dispatch the event |e| which bubbles and is cancelable, and which
			uses the {{ClipboardEvent}} interface, at |target|.

			Implementation requirements for access to data during event
			dispatch are defined in [[!HTMLLS]]. Some additional clipboard
			event-specific processing rules are given below:

			Issue: Why here? Why not in the HTML spec?

			1. If a script calls <a>clearData()</a> or
				{{DataTransferItemList/clear()}} and the {{DataTransfer}}
				object's internal [=drag data store mode=] flag is
				<a lt="concept dnd rw">read/write</a>, then

				1. Set the |clear-was-called| flag to true. If an
					argument is given, add the argument to the
					|types-to-clear| list.

			1. If a script calls <a>setData()</a> or modifies items and the
				|clear-was-called| flag is true, then

				1. If the |types-to-clear| list is empty, then

					1. Set the |clear-was-called| flag to false, then

				1. Else, if <a>setData()</a>'s <code>type</code> argument or
					the new item's [=drag data item type string=] is
					found in the |types-to-clear| list, then

					1. Remove it from the list. If the list is now empty,
						set the |clear-was-called| flag to false.

			1. If a script calls <a>getData()</a> or accesses items in the
				{{DataTransferItemList}} and |clipboard-entry| is
				set, then

				1. Check that the clipboard data's sequence number matches
					|clipboard-entry|. If the clipboard no longer
					contains the same entry, set the {{DataTransferItemList}}
					object's internal [=drag data store mode=] to
					<a lt="concept dnd p">protected</a>.

			Advisement: Warning! A malicious script listening to a paste event may set
			up a never-ending loop in order to read what the user places on
			the clipboard in the future. On platforms where a clipboard
			sequence number is not available, other limitations should be
			implemented.

	</div><!-- algorithm -->

	<div class="algorithm" data-algorithm="process-an-html-paste-event">
	<h3 id="to-process-html-paste-event"><dfn>process an HTML paste event</dfn></h3>

		: Input
		:: |clipboard-part|, the clipboard part to process
		:: |clipboard-event-data|, the {{DataTransfer}} object for this event

		: Output
		:: None

		1. Let |new-data| be a new {{DataTransferItem}} with
			[=drag data item kind=] set to <em>Plain Unicode string</em>,
			[=drag data item type string=] set to <em>text/html</em> or
			<em>application/xhtml+xml</em> accordingly.

		1. Extract the markup from |clipboard-part| and use the relevant parser to
			construct a DOM tree.

		1. If the markup's source URL is known, then resolve all relative URLs in
			HREF and SRC attributes using the source URL as base URL, and set the
			respective attributes to the resolved absolute URL.

		1. If the markup's origin is from a local application, then check whether
			there are references to local files and/or other parts of the OS
			clipboard's contents. If such references are found, references to
			sub-parts <em>must</em> be replaced by content-id references using the
			cid: URL scheme [[!RFC2392]]. To do so, process each attribute
			referencing a local file or clipboard part according to the following
			steps:

			Issue: Are these steps necessary? Do we know about native (platform)
			clipboard implementations that support multiple parts with internal
			references?

			Issue: This feature is at risk because it's unclear whether it is
			required, and because it's hard to test in a cross-platform way.

			1. If |clipboard-event-data|'s {{DataTransfer/items}} already
				contains an entry for the referenced file or clipboard part, then

				1. Set |itemNumber| to the index of the existing
					entry.

			1. Else,

				1. Let |new-file-data| be a new {{DataTransferItem}} with
					[=drag data item kind=] set to "file", and
					[=drag data item type string=] set to the MIME type of
					the file or clipboard part if known, or
					<code>application/octet-stream</code> if the
					file's type is unknown.

				1. Let |file-info| be a new {{File}} object with {{File/name}}
					set to the name part of the HTML attribute contents,
					and {{File/lastModified}} set to the
					timestamp of the referenced file or 0 if the entry
					references a clipboard part.

				1. Set |new-file-data|'s internal {{File}} object to |file-info|.

				1. Add |new-file-data| to |clipboard-event-data|'s {{DataTransfer/items}}
					and let |itemNumber| be the index of this entry in the
					{{DataTransferItemList}}.

			1. Update the DOM attribute that referenced the local file or
				clipboard part to contain the string 'cid:' followed by
				|itemNumber|.

		1. Serialize the processed DOM and update |new-data| with the resulting
			HTML code.

		1. Add |new-data| to |clipboard-event-data|'s {{DataTransfer/items}}.


	</div><!-- algorithm -->