Can anyone explain html5 'DOM' mode to me?

I am duplicating an archived topic from here:

As @mrcdk said, using -Ddom will utilize the browser DOM instead of a single browser canvas in order to render. Depending on your project and target device, this can perform much better – particularly for static content, heavy amounts of text, and slow TV browsers, particularly.

When you create a Sprite that renders to the screen, it may create a canvas element. A Bitmap will use either an Image or Canvas, based on whether the BitmapData was created at runtime or modified.

If you use “bitmapData.draw” with a single BitmapData, you actually can use the combined canvas approach that OpenFL uses by default, while allowing flexibility in having more static background graphics, or other DOM elements (such as using the OpenFL “DOMSprite” class) in front or behind your content.

You asked about testing in other browsers, when you run the “test” command, it should boot up a local webserver, and open using a “localhost” URL. Copy this URL to another browser while the “test” command is still running, and it should work fine.