I copied some code from a web page and into my text editor.
The double quote characters changed to this:
<iframe src=“http://www.yahoo.com” style=“width:500px; height:500px;” frameborder=“0?></iframe>
instead of this (which is what I needed):
<iframe src="http://www.yahoo.com" style="width:500px; height:500px;" frameborder="0"></iframe>
Why?