This plugin is useful if you want to ensure that the headings marked up with Textile inside an article body are all subheadings of the article title.
For example, your template might define the article title as an <h3> heading. If the author of the article used Textile
h2. headings, these would then break the hierarchy of heading levels. Presumably you would want the first subheading in the article body to be
h4. so that it is a proper subheading of the article title <h3>.
img_rebase_headings looks to see what is the top-level heading used in the article and adjusts all of the headings and subheadings found so that the top-level heading used matches the desired base level.
<txp:img_rebase_headings base="4"><txp:body /></txp:img_rebase_headings>