How does php clear echo content?

How does php clear echo content such
For example

Echo "how to delete this sentence! ";
?>

Delete the above sentence from the displayed webpage!

Reply to discussion (solution)

Script window. onload = function () {document. getElementById ("main"). innerHTML = "";} script

Use js and assign an empty value to id = "main"

How can I delete a button?

Just add a button and click the button again.

Script
Function foo (){
Document. getElementById ("main"). innerHTML = "";
}
Script