Add support for GitHub-style alert

[guoPhineas]

WIP

• Previous PR: Adapt for Swift 6.4 and add supports for Github-styled alert and streaming animation #156

[guoPhineas]

2026-07-27.10.45.37.mov

Hello,

This PR is ready for review.

I added .markdownQuoteAlertEnabled() to enable this style:

Thanks.🤝

[ajram23]

Love it. Hope this gets added!

[LiYanan2004]

Sorry for the delay. Reviewing now!

[LiYanan2004]

@guoPhineas Two issues:

• MarkdownText does not support this new view modifier (I fixed that)
• There are some edge cases for GitHub-style alert parsing (added some test cases for you) Please fix and make sure they are all passed)

[LiYanan2004]

This test fails

[LiYanan2004]

this test fails

[guoPhineas]

@LiYanan2004
Never mind for delay. Thanks for review.

I just fixed the issues you raised. But the test isn't also passed. I speculate that there may be code logic issues with the current testing:

The .multipleParagraphs test appears to have an issue in its body-extraction logic.

For this fixture, Swift Markdown produces the following AST:

• First Paragraph: [!NOTE] followed by First paragraph.
• Second Paragraph: Second paragraph.

However, when there is more than one child, the test uses:

bodyChildren = Array(children.dropFirst())

This discards the first paragraph, including First paragraph., and then asserts that the rendered body contains First paragraph.. Those two operations conflict.

The renderer should strip the alert marker/title line from the first paragraph, preserve the remaining inline content, and then append the remaining blockquote children. The implementation now follows that behavior, but the test’s extraction logic would need the same adjustment.

So, I fixed the issue in commit cf6e19a, how about this? It was passed on my Mac.