Mark WontFix since document.queryCommandSupported('paste') always returns true[1].

Please use document.queryCommandEnabled('paste') to check whether 'paste' command
is enabled or disabled.

[1] https://w3c.github.io/editing/execCommand.html#supported-commands

No, the command must "not be supported per:

"A command that does absolutely nothing in a particular user agent, such that execCommand() never has any effect and queryCommandEnabled() and queryCommandIndeterm() and queryCommandState() and queryCommandValue() each return the same value all the time, must not be supported."

So this issue should be fixed and supported should return false, as Edge, Firefox, and Safari do, because the paste command does nothing.

Could you file an issue to w3c editing issue tracker[1]?
Since, the spec is ambiguous, w3c editing task force should make the spec clear.

It seems WebKit checks clipboard access for queryCommandSupported('paste')[2]

There are similar discussion for queryCommandEnable('copy')[3]


[1] https://github.com/w3c/editing/issues
[2] https://trac.webkit.org/changeset/74580/webkit/trunk/WebCore/editing/EditorCommand.cpp
[3] https://github.com/w3c/editing/issues/161

I've filed an issue with the w3c editing task force here:
https://github.com/w3c/editing/issues/167

In my opinion, I do not believe what Chrome does is correct. The problem with queryCommandEnable is that it doesn't apply to buttons like it does context menu's. For a clipboard button you would want the button to focus the widget, if it's not focused, before performing its command. The user expects that clicking the button will focus the list/tree/etc.

This is perhaps best demonstrated by the WAI-ARIA listbox example:
https://www.w3.org/TR/wai-aria-practices/examples/listbox/listbox.html

In the case that what the button performs is not supported (such as a clipboard action) you would want to disable the button.

I just got a response from the W3C editing task force and they have confirmed that Chrome's behavior is in fact a bug and non-compliant with the standard:

https://github.com/w3c/editing/issues/167#issuecomment-327293494
https://www.w3.org/2017/09/05-editing-minutes.html

Mark Available to pick this up by someone regarding to #c6 

I will take this up

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/29e7204c4d91b754fe8df8e264695a695a5ab974

commit 29e7204c4d91b754fe8df8e264695a695a5ab974
Author: tanvir.rizvi <tanvir.rizvi@samsung.com>
Date: Fri Sep 15 08:06:44 2017

Update queryCommandSupported for paste command

Currently queryCommandSupported('paste') always
returns true, even when execCommand('paste') fails,
As per the recent spec updates[1] queryCommandSupported
should return false if the environment do not support.

[1] https://w3c.github.io/editing/execCommand.html#supported-commands

Bug: 757140
Change-Id: I42e8f645f46df632e38f8fe2a61a1143466a3387
Reviewed-on: https://chromium-review.googlesource.com/664777
Commit-Queue: Tanvir Rizvi <tanvir.rizvi@samsung.com>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#502199}
[modify] https://crrev.com/29e7204c4d91b754fe8df8e264695a695a5ab974/third_party/WebKit/LayoutTests/editing/pasteboard/copy-cut-paste-supported.html
[modify] https://crrev.com/29e7204c4d91b754fe8df8e264695a695a5ab974/third_party/WebKit/Source/core/editing/commands/EditorCommand.cpp