Highlights, Labels, or Replaces text/regex match.
In Label mode, the text is not highlighted, but tooltips are visible when hovering over matched text (if a label is present).
In Highlight mode, the text is highlighted, and tooltips are visible when hovering over matched text (if a label is present).
In Replace Mode, the replacement can be text, or a regex replacement consisting of groups (eg: <a href="?q=$1">$2</a>)
Note: Reordering rows may help when you have many complex regex replacements.