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Xoc - 11:11 pm on Apr 19, 2001 (gmt 0)
What a web browser really does with markup that isn't in the DTD is it probably renders it using the current rules. But that's not what it's supposed to do. You should conform to what the HTML spec for what you are doing says. If you can't make your document validate, don't put any DOCTYPE specification. Then the web browser will guess what HTML you are doing. I recommend using this DTD for the moment: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "DTD/xhtml1-transitional.dtd"> But that requires using XHTML 1.0.
You should use the DOCTYPE that matches the HTML tags and attributes that you are using. When you specify the DOCTYPE, you are actually identifying a particular DTD (Document Type Definition) file on the web (for example, [w3.org ]) that it compares the rest of the HTML file to. Any tags or attributes that are defined in the DTD are supposed to be interpreted. Any tags or attributes that are not in the DTD are supposed to be ignored, but the text inside the tags rendered. So if you use the DTD for HTML 2.0, <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">, then you shouldn't be able to use any of the features from HTML 3.2, 4.0, 4.01, or XHTML 1.0 that weren't supported in HTML 2.0.