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Headings provide readers with an outline of a document. Users can jump from heading to heading and can see what is going to be in the document without having to read it all. Headings are have six levels of tags. <H1> through <H6>. These tags are important because they establish part of the hierarchy. An <H1> tag should always be above the rest of the heading tags. An <H6> tag is always the lowest heading tag. Heading 1 level tags are always labeled with a name for a section or sometimes a title. The lower heading tags are for sections within a section. Hence the importance of the hierarchy.
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