Lars Heber writes:

<dtml-let text="my html text with a link to <a href="http://www.yahoo.com">Yahoo!</a>"> <dtml-let text="'my html text with a link to <a href=\x22http://www.yahoo.com\x22>Yahoo!</a>'">

I.e. you use Python's hexadecimal (or octal) quoting for '"' (\x22) inside the Python string. Dieter