Search Engine Optimization is one of the musts for a web site. There are many ways to keep good SEO, like those that we all know: only one H1 in each document, using good keywording, etc.
For websites offering a search feature, it's good to show some links to common or important searches. The common "cloud of tags" is a good example; they provide links to page with search results.
But when happens when we don't have any result on such pages? Let's say we have a tag "expired", and we have there all the documents, products or posts that we consider expired, but we still want to be available to the users, so we keep the content on line. In this case the search for "expired" will return documents. One good day we decide to not show those results anymore, so the page /search/expired, which was already indexed by all search engines, now will simply show "Sorry, but there are no results for your query".
To solve that we have an excellent tool that we can use. Instead of returning the "200 OK header", we'll return "404 Not found", but we'll still show a page saying "There are no results, but a lot of suggestions". Then we'll offer different options, but our page won't be indexed anymore in Google.
That's it... when no results are found for an indexed search URL, let's say when Google tries to index a ZRP -Zero result page-, you should reply with a list of suggestions and a nice "404 not found" header:
header("HTTP/1.0 404 Not Found");
This will ensure that no search engine will index that page.
