Search engines are getting smarter. You acknowledge xHTML tags not only to filter out text contained herein or any attributes for indexing, but they also know their semantic meaning. Of particular importance are heading, but if they only <h1> to <h6> or <th> are logically distinguished as such, mere visual highlighting is not enough of this. However, do not try to set all the important keywords in <h1>.
One side usually has only a header level, and therefore an inappropriate use reduce the relevance of this distinction, but it could also be interpreted negatively as an unwanted search engine spamming. Moreover, <h1> usually makes sense to use only as the page heading. To highlight important keywords in the text provided for this purpose you should xHTML elements < strong > and <em> use you can format via CSS. Avoid the bare optical highlighting e.g. <font>, but also about <b>, even if here, after all the desire to emphasize is clear.
Search Engines work by clear structuring of the source code with no superfluous elements. The content should have a significantly higher proportion than the xHTML elements, which also keeps the loading time. Related text paragraphs should be provided for this purpose in the < p > tags are placed. Between headings in <h2> to <h6> can highlight more keywords and facilitate the orientation (even if search engines currently are perhaps not so far, to use all these tools). Menu links are best used in an <ul> set list and like all the other elements – formatted by CSS.
The unknown element <link>
They have heard nothing about it. Then they are just as ignorant as unfortunately the search engines. About the <link> -item relationships to other sources can <head> an xHTML file can be specified. Unfortunately, many browsers do not interpret even this. If you do not see these links, you should maybe switch to a modern browser, for this convenience is now available to you on more and more websites.