__Web Messaging__ or __cross-document messaging__, is an API introduced in the WHATWG HTML5 draft specification, allowing documents to communicate with one another across different origins, or source domains while rendered in a web browser - wikipedia 
This HTML5 technology is built into modern browsers and uses the Window.postMessage method.
# Security
Prior to HTML5, web browsers disallowed cross-site scripting, to protect against security attacks. This practice barred communication between non-hostile pages as well, making document interaction of any kind difficult.
Cross-document messaging allows scripts to interact across these boundaries, while providing a rudimentary level of security.
# Alternative
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# Sections
# See also