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Placing Hyperlinks in Web Content

There's no need to hyperlink every instance of a word or phrase in the same page. Generally, linking to the first instance will do.

There are a couple of exceptions to this rule:

The page is very long, and the anchor text appears in multiple places in the page.Link one anchor approximately every 1.5 screen pages.
You need to convey certain information before the user leaves the page.Link the first instance after that information.

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