Placing a text form into a variable

I created a text box form in one of my Twine passages using HTML5 syntax. It looks like this:

<input type="text" name="your name" size="30">

How can I place user's input text into a variable?
The following construction with parentheses doesn't work:
(set: $yourName to (<input type="text" name="your name" size="30">))

I don't want to use any pop-up windows with a 'prompt:' command, just a simple text box form.

Please help me!