Posts a message that is a simple string rather than a JSON string
representation of a JavaScript object. This behaves in exactly the same
manner as PostWebMessageAsJson, but the data property of the event
arg of the window.chrome.webview message is a string with the same
value as webMessageAsString. Use this instead of
PostWebMessageAsJson if you want to communicate using simple strings
rather than JSON objects.
The D Programming Language's Unofficial Docs
beta
Posts a message that is a simple string rather than a JSON string representation of a JavaScript object. This behaves in exactly the same manner as PostWebMessageAsJson, but the data property of the event arg of the window.chrome.webview message is a string with the same value as webMessageAsString. Use this instead of PostWebMessageAsJson if you want to communicate using simple strings rather than JSON objects.