Hi, Is there is any difference between <span class="header">keyword</span> AND <H1>keyword</H1> Which one is useful in the eyes of search engine spider.
The differences are that <h1> is defined in HTML syntax as a header with the greatest significance (over h2, h3, etc.). The other in your example is not a "header" tag, it's a <span> tag with a class called "header". You could have called it anything that you wanted. If SE's even consider classes given to tags, then the best would have to be a <h1> with a header class, i.e. <h1 class="header"> but I doubt it would help.
Are you talking about strictly SEO or does this deal with CSS? If this has to do with style then why not use inline style? If this is an SEO question then why not spend the extra time you would have used on code developing content?
You can use: <h1 class="t11">Keyword</h1> Code (markup): In your css file: .t11{ /* Include your t11 styling here */ } Code (markup): And yes, H1 has more weigh