Search code examples
dhtmldoctype

What are the dangers of not conforming to declared HTML doctype?

I have an ASP.NET MVC 2 web site, the site.master declares

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

but in the code I have

<td class='count-col' data-object-id='<%= Model.ObjectId %>'>
  1. Am I correct that attribute data-object-id is not valid in the declared doctype (XHTML)?
  2. What are the downshots of having that violation?
  3. What is a good solution for this situation? Should I change DOCTYPE (what would be drawbacks)? Or should I come up with a different way to specify object-id on the element?

Note: object-id is used by a javascript function that shows a popup on <td> hover.

Solution

  • It could give "unexpected" behaviour in older browsers, yet most browsers render it anyways. That, and your code won't validate, though that should in the real world not really stop you.