Spaces in the URL fragment are invalid; encode them or remove them (e.g., use %20 or hyphens/underscores).
The href attribute must contain a valid URL. When using a fragment identifier (the part after #), it must follow URL syntax rules: no unescaped spaces. Fragments usually reference an element’s id. An element’s id must be unique and is case-sensitive; while spaces aren’t allowed in id values, many authors accidentally mirror text with spaces in the fragment. Use hyphens or underscores in ids and match the fragment, or percent-encode reserved characters. Prefer readable, dash-separated ids for accessibility and shareable links.
For example, instead of href=”#My Section”, use href=”#my-section” and set id=”my-section” on the target. If you must preserve spaces in a generated URL, encode them as %20, but it’s better to avoid spaces entirely in ids.
HTML Examples
Invalid: reproduces the validator error
<!doctype html>
<html lang="en">
<head>
<title>Fragment with space</title>
</head>
<body>
<a href="#My Section">Go to section</a>
<h2 id="My Section">My Section</h2>
</body>
</html>
Fixed: use a valid fragment and id
<!doctype html>
<html lang="en">
<head>
<title>Valid fragment</title>
</head>
<body>
<a href="#my-section">Go to section</a>
<h2 id="my-section">My Section</h2>
</body>
</html>
Alternatively, encoding the space also passes validation, though less ideal as the id would be invalid because it contains spaces:
<a href="#My%20Section">Go to section</a>
<h2 id="My Section">My Section</h2>