line 1 column 1 - Warning: missing <!DOCTYPE> declaration
line 6 column 1 - Warning: missing </font> before <h1>
line 6 column 23 - Warning: inserting implicit <font>
line 6 column 39 - Warning: discarding unexpected </font>
line 10 column 1 - Warning: missing </span> before <h1>
line 10 column 23 - Warning: inserting implicit <span>
line 10 column 39 - Warning: discarding unexpected </span>
line 6 column 1 - Warning: trimming empty <font>
line 10 column 1 - Warning: trimming empty <span>
line 6 column 23 - Warning: <font> element removed from HTML5
line 10 column 23 - Warning: <span> proprietary attribute "color"
Info: Document content looks like XHTML5
Tidy found 11 warnings and 0 errors!

You are recommended to use CSS to specify the font and
properties such as its size and color. This will reduce
the size of HTML files and make them easier to maintain
compared with using <FONT> elements.

One or more empty elements were present in the source document but
dropped on output. If these elements are necessary or you don't want
this behavior, then consider setting the option "drop-empty-elements"
to no.

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