What is difference SEO differencence between:
The fragment identifier (when dealing with the URI of an HTML document) is supposed to be used to link to specific parts of a page. It isn't sent to the server.
In the last few years it has been used as a hack to maintain state information in websites that make heavy use of Ajax.
The use of a fragment identifier starting with a
The introduction of pushState eliminates the need for these hacks in modern browsers.
For browsers that don't support
The exclamation point, eliminates the case of an empty hash like