The Header Tags plugin gives you more control over the heading tags (h1-h6) in your website. The plugin searches for existing heading tags within the selected content area and handles them according to your specifications. So if want all the H4 tags in your site to be changed to H3, you can!
The default behaviour after installing the plugin, is checking if there is a H1 tag in the output of the component. If none are found, the plugin changes the first H2 tag into a H1.
The content area is where the plugin searches for heading tags. The component output is like the main content section of your website. This way the plugin ignores any heading tags which may exist in your template or modules. If you want to control ALL the header tags of your website, select entire page.
For each tag you can specify if the tag is mandatory, so the tag should exist at least once. If it doesn’t, you can select from which tag the first one should be changed.
You can also select how many times a tag is allowed, and to what the excess tags should be changed to.
The Header Tags page on the Conflate site: http://www.conflate.nl/joomla-extensions/header-tags.html