Tag Type C++ code (built in to libHForm/scan_body.cc)
Attributes var=varName Required. Sets the variable which will contain the block of text entered in the TextArea widget.
rows=integer Optional. Sets the number rows in the text box.
cols=integer Optional. Sets the number columns in the text box.
Contained Tags None.
Related Tags This tag must appear in the Body section. It is a multi-line version of the Entry widget.

A typical box for comments on form can be created with something like this:
  {TextArea var=comments cols=72 rows=6}
And if the form is submitted with an Exec that uses method=env, for example, a shell script could e-mail the comments using a script like this:

cat <<EOF | sendmail -t -O DeliveryMode=i
From: $firstname $lastname <$email>
To: webmaster@yourdomain.org
Subject: Comments from the Web

Note that "comments" must be declared in the Public section in order to be exported, as usual. Also, the shell must support environment variables with embedded newline characters (bash does.)