Editor: The Safari Tidy plugin is a small plugin that lets you validate the webpages you browse for (x)html compliance. The actual validation is done by Tidy. This plugin was modeled after a similar plugin for Firefox, which can be found here. How it works
In the bottom right corner of each browser window you will see the amount of warnings and errors the current page has, along with a small icon.
Clicking on the icon will show the source of the current page. The default 'view-source' window of Safari is extended so that it shows all the errors and warnings in a list. The lines containing errors are highlighted so they can be located easily. Doubleclicking on a warning or error in the list will position the cursor at the correct location in the html source text.