Why we need bang mark in hash navigation URLs?

Question

We are developing SPA with hash tag navigation. Saw on another SPA sites there is hash tag URLs like http://example.com/#!/users Our application currently implements hash tag URLS without ! (bang, exclamation mark) like http://example.com/#/users Is there some reason for using bang mark in URL? I've checked few SO questions, some documentation: URL hash-bang (#!/) prefix instead of simple hash (#/) in Angular 1.6 People want to get rid of exclamation mark in their SPAs.

However, Angular Changelog states it was significant change to add bang mark in URLs: https://github.com/angular/angular.js/blob/master/CHANGELOG.md#location-due-to

Google's documentation also shows an examples with exclamation marks: https://developers.google.com/webmasters/ajax-crawling/docs/getting-started

My main question is - for what we need exclamation mark in hash URL? Does it makes any sense?

Thanks in advance for answers!

Answer 1

RFC 3986 specifies that a URL fragment starts with a hash. A fragment references typically a HTML anchor. And HTML 4 defines that the ID of a HTML anchor must not contain a bang.

If you want to be sure that your tags do not collide with HTML anchors, it might be useful to mark the tags with the bang.