w3c validation
The World Wide Web Consortium (W3C) provide more than just guidance. It is now possible to check your page quite simply on-line.
What can w3c check?
The three main services are to check a page's html code for errors, to check CSS stylesheets for use of current tags rather than older ones no longer widely supported and to search for broken links. A nice touch is something they call html tidy which can be used to correct many errors found. There may still be some work for the author to do and the correction method used may not be quite what you want but it can be a quick solution where validation is important.
There are many types of code for which standards are either ready or in preparation - the later ones applying to recent developments in coding such as automatic or programmed recognition of addresses, phrases and data.