The id attribute just got more awesome in HTML5

id=♥ + #♥ { background: lime; }
id=© + #© { background: lime; }
id=“‘’” + #“‘’” { background: lime; }
id=☺☃ + #☺☃ { background: lime; }
id=⌘⌥ + #⌘⌥ { background: lime; }
id=𝄞♪♩♫♬ + #𝄞♪♩♫♬ { background: lime; }
id=? + #\? { background: lime; }
id=@ + #\@ { background: lime; }
id=. + #\. { background: lime; }
id=:) + #\3A \) { background: lime; }
id=:`( + #\3A \`\( { background: lime; }
id=123 + #\31 23 { background: lime; }
id=1a2b3c + #\31 a2b3c { background: lime; }
id=<p> + #\<p\> { background: lime; }
id=<><<<>><> + #\<\>\<\<\<\>\>\<\> { background: lime; }
id=++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>. + #\+\+\+\+\+\+\+\+\+\+\[\>\+\+\+\+\+\+\+\>\+\+\+\+\+\+\+\+\+\+\>\+\+\+\>\+\<\<\<\<\-\]\>\+\+\.\>\+\.\+\+\+\+\+\+\+\.\.\+\+\+\.\>\+\+\.\<\<\+\+\+\+\+\+\+\+\+\+\+\+\+\+\+\.\>\.\+\+\+\.\-\-\-\-\-\-\.\-\-\-\-\-\-\-\-\.\>\+\.\>\. { background: lime; }
id=# + #\# { background: lime; }
id=## + #\#\# { background: lime; }
id=#.#.# + #\#\.\#\.\# { background: lime; }
id=_ + #\_ { background: lime; }
id={} + #\{\} { background: lime; }
id=.fake-class + #\.fake\-class { background: lime; }
id=foo.bar + #foo\.bar { background: lime; }
id=:hover + #\3A hover { background: lime; }
id=:hover:focus:active + #\3A hover\3A focus\3A active { background: lime; }
id=[attr=value] + #\[attr\=value\] { background: lime; }
id=f/o/o + #f\/o\/o { background: lime; }
id=f\o\o + #f\\o\\o { background: lime; }
id=f*o*o + #f\*o\*o { background: lime; }
id=f!o!o + #f\!o\!o { background: lime; }
id=f'o'o + #f\'o\'o { background: lime; }
id=f~o~o + #f\~o\~o { background: lime; }
id=f+o+o + #f\+o\+o { background: lime; }

As the spec says…

Attributes are placed inside the start tag, and consist of a name and a value, separated by an = character. The attribute value can remain unquoted if it doesn’t contain spaces or any of " ' ` = < or >. Otherwise, it has to be quoted using either single or double quotes. The value, along with the = character, can be omitted altogether if the value is the empty string.

Note that instead of “spaces”, it should really say “whitespace” there. (Bug #12938)

At this point, there are only four validation errors on this page – can you spot them?

By now the validation error count is going through the roof.