A system allows modules associated with different domains to communicate, such as within a container document. To transfer payload data from the first module associated with a first domain to a second module associated with a different domain, the first module adds the payload data as a text string to the URL of a transport module associated with the second domain. This way, the second module may directly access the modified transport module to obtain the payload data from its URL. The second module may likewise add other payload data as a text string to the URL of another transport module associated with the first domain, thereby enabling communication from the second domain to the first.