__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
* Use cookies - stackoverflow
We have released a new version of the Frame plugin (v0.7.0) which allows framed content to interact with the hosting wiki in interesting ways.
We collect here a few javascript libraries which build on top of the postMessage API to enable cross-origin communication. Be begin this journey with experiments to enable wiki integrations via the Frame Plugin. What we found along the way invite other design questions.
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