We are going to update our website from well-formed XHTML 1.0 Transitional to HTML 5. However, as I see, we will be doing this step-by-step. This means we will have some pages in HTML 5 and others in XHTML at the same moment. Can it affect our current SERP positions and the results of other SEO works we have already done?


2 Answers 2


This means we will have some pages in HTML 5 and others in XHTML at the same moment.

Having some pages in your site marked up with HTML5 and some in XHTML should not be a factor in your site's ranking since search engines crawl and index pages individually.


Unless you're going to dynamically serve the relevant doctype for either HTML5 or XHTML then you'll likely have a lot of W3C invalid markup during the update process and whether this affects the performance of your website (SEO) is answered here.

What you should be doing is setting up your website as a development stage and completing all the work before pushing it live. This avoids countless potential issues.

  • 3
    From the question it would seem that pages will either be marked up as valid XHTML 1.0 (text/html I assume) or valid HTML5 - this shouldn't result in any invalid markup. The OP seems to be asking whether having a mix of different page types would be a problem?
    – MrWhite
    Jan 31, 2014 at 15:49
  • @w3d, Our website has say 20 pages. 12 of them will be marked as HTML 5, the others will remain XHTML 1.0 Transitional. Every page will have just only one <doctype> directive.
    – TecMan
    Jan 31, 2014 at 16:04
  • So this would result in invalid markup then unless the doctype will be dynamically served for each page each stage of the update process. Unless they are static pages and the doctype is manually at the top of each then it doesn't matter.
    – zigojacko
    Jan 31, 2014 at 17:13
  • Why are you talking about dynamic doctype? We can consider our pages as static (though they come from the ASP.NET engine). Sure, I do understand that having a lot of markup errors can worsen our SERP positions dramatically :).
    – TecMan
    Feb 3, 2014 at 13:54
  • what Geoff Jackson means, is that on your server you have something that is in charge to send the correct mime-type for each document, either the web server, or a language like perl, php, etc. He is focusing the answer from the perspective that if you send, for instance, all the documents as text/html, technically, you may be sending xhtml wrongly since it should be application/xhtml+xml when using the strict mechanic.
    – PatomaS
    Feb 5, 2014 at 1:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.