$compileProvider.aHrefSanitizationWhitelist()

Retrieves or overrides the default regular expression that is used for whitelisting of safe urls during a[href] sanitization.

The sanitization is a security measure aimed at preventing XSS attacks via html links.

Any url about to be assigned to a[href] via data-binding is first normalized and turned into an absolute url. Afterwards, the url is matched against the aHrefSanitizationWhitelist regular expression. If a match is found, the original url is written into the dom. Otherwise, the absolute url is prefixed with 'unsafe:' string and only then is it written into the DOM.