line 1 column 1 - Warning: missing <!DOCTYPE> declaration
line 6 column 1 - Warning: <a> attribute with missing trailing quote mark
line 6 column 1 - Warning: <a> escaping malformed URI reference
line 6 column 1 - Warning: <a> illegal characters found in URI
Info: Document content looks like HTML5
Tidy found 4 warnings and 0 errors!

URIs must be properly escaped, they must not contain unescaped
characters below U+0021 including the space character and not
above U+007E. Tidy escapes the URI for you as recommended by
HTML 4.01 section B.2.1 and XML 1.0 section 4.2.2. Some user agents
use another algorithm to escape such URIs and some server-sided
scripts depend on that. If you want to depend on that, you must
escape the URI on your own. For more information please refer to
https://www.w3.org/International/O-URL-and-ident.html

About HTML Tidy: https://github.com/htacg/tidy-html5
Bug reports and comments: https://github.com/htacg/tidy-html5/issues
Official mailing list: https://lists.w3.org/Archives/Public/public-htacg/
Latest HTML specification: https://html.spec.whatwg.org/multipage/
Validate your HTML documents: https://validator.w3.org/nu/
Lobby your company to join the W3C: https://www.w3.org/Consortium

Do you speak a language other than English, or a different variant of 
English? Consider helping us to localize HTML Tidy. For details please see 
https://github.com/htacg/tidy-html5/blob/master/README/LOCALIZE.md