$w('#html1').postMessage("<html>Hi!</html>"); shows nothing

Hey stone,

You can’t paste HTML code in a text box - it goes in an HtmlComponent.

I would recommend reading the article Working with the HTML Component in Wix Code . There is also a very nice and simple example in the description of the onMessage() function - just scroll down a bit to find it. Try this example yourself and then you can modify it for your own use.

Good luck and have fun,

Yisrael