The #! declares to crawlers that a crawlable version of the page is also available from the server by replacing "#!" with "?_escaped_fragment=". This mapping i

The #! declares to crawlers that a crawlable version of the page is also available from the server by replacing "#!" with "?_escaped_fragment=". This mapping is needed because the fragment string is never passed to the server, so it has to be encoded elsewhere and the query section is the only available place. The "!" is needed because otherwise crawlers would start fruitlessly hammering all the existing sites that use '#' but don't support the '?escaped_fragment=" hack.