Markdown Syntax of Strikethrough Highlighting mismatch with preview.

[laazy]

We have written the needed data int
Issue Type: Bug

1. type ~delete word~
2. it displayed in editor as delete word, same as the github deal with single tilde
3. click open preview, it shows as ~delete word~

As vscode documents mentioned,

VS Code targets the CommonMark Markdown specification using the markdown-it library.

Vscode editor should not treat single tilde as strikethroug according to markdown-it, and it should act same with preview window.

VS Code version: Code - Insiders 1.67.0-insider (8b7086a, 2022-04-01T05:16:02.350Z)
OS version: Windows_NT x64 10.0.19044
Restricted Mode: No

System Info

Item	Value
CPUs	AMD Ryzen 5 3600 6-Core Processor (12 x 3593)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: disabled_off direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on oop_rasterization: enabled opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_renderer: enabled_on video_decode: enabled video_encode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled
Load (avg)	undefined
Memory (System)	15.95GB (1.94GB free)
Process Argv	--crash-reporter-id 3ca66572-e046-4df9-bfdd-5f4e15550577
Screen Reader	no
VM	0%

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[laazy]

what it looks like:

[babakks]

@mjbvz I've just submitted a PR for this.

[Lemmingh]

Though I also feel very strange about this single-tilde-strikethrough, there are explicit test cases for it.

• Add strikethrough support vscode-markdown-tm-grammar#101

I guess it would be best to discuss with the original contributor first, even if it's just a mistake.

[mjbvz]

@Lemmingh It's likely an oversight. If the common mark spec says to use two tildes, that's what we should support

[Lemmingh]

Yeah, GFM requires two tildes:
https://github.github.com/gfm/#strikethrough-extension-

[Lemmingh]

Um, interesting fact:

GFM requires "two tildes", but cmark-gfm still accepts "single tilde", which is an intentional mismatch for backward compatibility and causes confusion between implementations.

• https://github.com/github/cmark-gfm/blob/cf7577d2f74289cb83de0a652afc1a8b08a37036/test/extensions.txt#L502-L533
• Strikethrough by double tildes github/cmark-gfm#71
• Markdown strikethrough is not limited to two tilde wrapping markedjs/marked#1561 (comment)

Still, aligning with the spec should be the right way.