In the ignore_content_by_css_selector key of the site-search config file, you can specify CSS selectors of elements that should not be indexed. By default, the content of a nav element will not be put in the index (but all URLs inside it will still be crawled).
Additionally, any elements with a data-no-index will not get indexed. In the following example, the sentence "This will not be indexed", will not be indexed.
<html> <head> <title>This is my page</title> <metaname="description"content="This is the description"> </head> <body> <nav> This is the content of the nav. It should not be indexed. </nav> <h1>This is the H1</h1> This is the content <divdata-no-index> This will not be indexed. </div> </body></html>