[Plugin: Contact Form 7] how to add watermark to text field?

Hi. I’m trying to add a watermark to a text field. The instructions say:

watermark Use the value as watermark text instead of as default value.

but I don’t know the syntax. I’ve tried

watermark:”[email protected]”
watermark “[email protected]”
watermark:[email protected]

and a few others I thought would work, but all examples produce default values instead of watermark text.

Any suggestions?