What is the Ajax crawling scheme specification?
How does the Ajax crawling scheme work?
When a page depends on JavaScript to be rendered and properly indexed, a special tag
<meta name="fragment" content="!"> is added in the <head> of the page. When a
bot detects the presence of this tag in a page, it requests the same URL by appending the query parameter
the _escaped_fragment_= to
retrieve the corresponding snapshot.
This behavior has been officially deprecated. Today, it is recommended to make sure your site implements a new recommendation called "Dynamic Rendering".