Starting in 1996, Alexa Internet has been donating their crawl data to the Internet Archive. Flowing in every day, these data are added to the Wayback Machine after an embargo period.
The level 4 heading
should be rendered more prominently than a H5, but less prominently
than a H3. It is often used to mark up subsections in a document.
The optional ALIGN attribute controls the horizontal alignment of the header.
It can be LEFT, CENTER or RIGHT.
Notes:
Headers should be used in hierarchical order.
Do not assume that this header means "large font size and
bold." While this is a popular rendering, it can be anything the browser
chooses.
Search engines may give words appearing in headers more importance
in their index. The headers are also often used to build an "outline"
of the document, which appears in the search results.
Right alignment is not as widely supported as centered.