Document Windows file path handling in URL parsing (WHATWG URL #874)

[mertcanaltin]

What information was incorrect, unhelpful, or incomplete?

The URL API documentation should be updated to reflect the
new Windows file path handling feature being added to the
WHATWG URL specification.

What did you expect to see?

Documentation explaining that Windows drive letter patterns
(like C:\folder\file.txt) are automatically converted to
file:/// URLs when parsed.

Example

new URL("C:\\folder\\file.txt")
// Returns: file:///C:/folder/file.txt

Implementation status

Implementation bugs have been filed:

• Chromium: https://issues.chromium.org/issues/437449112
• Gecko: https://webcompat.com/issues/170937
• WebKit: https://bugs.webkit.org/show_bug.cgi?id=297169
• Deno: Implement Windows file path handling in URL parsing (WHATWG URL #874) denoland/deno#30363
• Node.js: Implement Windows file path handling in URL parsing (WHATWG URL #874) nodejs/node#59415

Related links

• Spec PR: feat: handle Windows file paths with backslashes in URL parsing whatwg/url#874
• Original issue: Windows file paths in URL parsing whatwg/url#873
• Tests:
  accepting windows backslash paths web-platform-tests/wpt#53459

This documentation update should be made once the spec
change is merged and browsers begin implementation.