The content of the first heading should be the same as or have a similar meaning to the title. Also, there are Web crawlers that index according to the content of specific tags, including headings and addresses. The ALT attribute lets you specify text to display for non-graphic browsers, and while images are loading in graphic browsers. At the top of each page, give a heading or graphic which summarizes that contents of the page. This orients users, and gives search engines something logical to index.
Emphasis is always relative.
There are many browser-specific extensions to the HTML 2.0 specification. There are many elements from the HTML 3.0 specification that people wish to use already. You must decide which extensions to use while still taking into account the large variety of Web browsers, platforms and user preferences. Use of certain extensions can make a page look great when viewed with one particular browser on a particular platform, and terrible with another, or even with the same browser but on another platform. Undeclared attributes are treated similarly.