This plugin makes the WordPress built-in search ignore HTML tags in post content.
By default, the WordPress built-in search considers HTML tags in post content to be searchable content. This behaviour often yields unexpected results. For example, a search for the keyword “strong” returns posts with any <strong> tags in them, “title” returns posts with any HTML tags that have a title attribute (such as all the <img> tags that you insert via the post editor media buttons)… and so on.