About This HTML Issue
A backslash (\) is not a valid character in a URL fragment and must be replaced with a forward slash (/) or percent-encoded.
The href attribute on an <a> element must contain a valid URL according to the URL Living Standard. The fragment portion of a URL — the part after the # symbol — follows the same rule: it can contain most characters, but the backslash (\) is explicitly forbidden as a bare character.
This commonly happens when copying file paths from Windows, which uses backslashes as directory separators, and pasting them into an href. Browsers may silently convert \ to /, but the markup is still invalid.
To fix this, replace every \ with / in the URL. If for some reason you actually need a literal backslash in the fragment, percent-encode it as %5C.
HTML Examples
❌ Invalid: backslash in the fragment
<a href="page.html#section\one">Link</a>
✅ Fixed: use a forward slash or percent-encoding
<!-- Option 1: Replace with forward slash -->
<a href="page.html#section/one">Link</a>
<!-- Option 2: Percent-encode the backslash -->
<a href="page.html#section%5Cone">Link</a>
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