With Yahoo the notable exception almost all of the main search engines use computer programs called 'spiders' or 'robots' to index sites automatically. Unfortunately these programs are not highly advanced and do not pick up any of the modern languages or techniques used in constructing web sites.
Spiders can only understand HTML code.
Some index the whole of the site and give extra ranking points for links on the site, some ignore any text which contain hyperlinks and some take the ranking from purely the first page and the main titles. Search engines also used to pick up and rank according to 'meta tags' which are placed in the HTML code of the index page. You require a high level of interactivity to provide the best level of service to your present customers on your web site however you also need to get a good search engine rank to drive new business to the site. Fortunately there are solutions to the problems that modern site construction present. While there are some simple fixes for problems such as frames a vast number of sites now involve more than one if not all interactive languages mentioned above.