HTML is a markup language for textual content . The award is undertaken through tags that are expressing a certain semantic meaning and rendered in a corresponding way of browser so that this importance is manifested visually for a visitor . About this award so it is possible that certain content be assigned semantics.
There is no official statement on what day how much weight is attached and you can assume that there are no simple mathematical relationships, but that make up a positive value for the ranking of different factors. It is not enough, all the keywords to highlight the text in bold for example, or even as a heading. Such techniques are considered rather as spam. The following are some examples of tags that have an impact on the ranking.
Headlines
Headings are identified in the <Hx> HTML tags, where x is the level of the heading. <h1> tags identify the main headings. The keyword or keyword combination should show up in any case within a <Hx> tags. However, one can make a clear statement as to whether Google uses different shades hour day in their natural order as ranking factors. Against this assumption, for example, that the world's most popular blogging system WordPress is the title of new posts by default in <h2> place in <h1> tags.
Some time ago it was also fashionable to use <h1> tags as a replacement for <b> or <strong> tags to benefit from the "header bonus". This is of course not in the sense of the user in terms of Google and still is considered rather as spam. Nevertheless, it is ok to have more than one <h1> day to use as Matt Cutts explained in the following screencast:
However, it is relatively safe to say that words in titles revert to a higher importance because they clearly stand out from the text. eye tracking analyzes have also shown that visitors mainly read the headlines and skim over the rest of the text. So it makes perfect sense to ascribe greater importance to these structuring elements.
Lists
Lists are also structuring elements and fall when viewing a web page in the eye. In Document ranking based on semantic distance between terms in a document different approaches and algorithms are presented which are intended to identify the semantic proximity of words in a text. One of these approaches is here that lists must be treated separately, as they could for example make a value-free bullets. For example, the data shown in the diagram below as equivalent with respect to the semantic distance on the titles to consider, although the last point considered purely localized further away than the first.
Bold, italic, etc.
Words that are marked in a manner within a continuous text that set it apart from the rest of the text stand out a visitor reading the eye. So these words seem to carry more significance than the non-selected words. At this point, the term "marker" but to widely used because it is possible through the introduction of CSS to create these visual effects, without using the provided HTML tags. A search engine can not understand this then highlighting.
Detectable influence according to Mario Fischer at least the award in bold or by <b> <strong> tags (Website Boosting 2.0, p 320). It is likely that the same for italics (or <i> <em> tags) and underlined text (<u> day) applies. <b> and <strong> and <i> or <em> tags are considered equivalent by the way, like Matt Cutts confirmed in the following screencast (from 0:48):
From the perspective of usability , it makes sense to highlight particularly the most important statements in a text so that a reader has only to skim the text if need to understand the core message.
Conclusion
What does that exploits in practice? The above examples and illustrations are intended only as an indication that Google assesses the HTML syntax of a text. For practical use, it lends itself to so that keywords and semantically related terms prepare accordingly.
