Why canvas is not a self closing HTML5 tag

While debugging a page produced by our PDF to HTML5 Converter, I noticed that Firefox was showing some of the tags in the HTML source in red.

Specifically, there was a closing div tag.

The solution I thought was quite obvious – there must be no opening div tag for it to close.
But scrolling up, indeed there was a div tag for it to close.

The problem itself was actually in the line above – the canvas tag.

The line used was <canvas id=”pdf15″ width=”1053″ height=”813″ />. Although our canvas tag has nothing inside it because of the way that the canvas works, that doesn’t mean that we are allowed to self close it like we would an <img />.

The reason that canvas tag requires a separate closing tag is because it’s actually possible to put content inside that will display instead of the canvas if the user’s browser does not support HTML5.

Problem solved!