What are all these "input hidden" entries for?

[Seijun]

At the top of my form, there is this:

<input type="hidden" name="recipients" value="pams9127f4nightowl.net" />
<input type="hidden" name="required" value="EmailAddr:Your email address,Name:Your name" />
<input type="hidden" name="derive_fields" value="email=EmailAddr,realname=Name" />
<input type="hidden" name="mail_options" value="Exclude=email;realname;your_good_url,KeepLines" />
<input type="hidden" name="subject" value="WRN Placement Form" />
<input type="hidden" name="good_url" value="" />

I understand "recipients", "required", and "subject", but I would love to know what the other stuff does. In particular, "email=EmailAddr,realname=Name".
It looks like this saying "treat 'email' as 'EmailAddr' and treat 'realname' as 'Name'." But what good is that doing? I see it corresponds to <input type="text" name="Name" /> and <input type="text" name="EmailAddr" /> later on in the form, but why not just change these to <input type="text" name="realname" /> and <input type="text" name="email" />, and then delete "email=EmailAddr,realname=Name"? Is there a reason these two particular fields are being given two names each?

[russellr]

Hi,

Please read the HOW TO guides for details:
http://www.tectite.com/fmhowto/derived.php
http://www.tectite.com/fmdoc/creating_forms.php

The purpose of deriving email and realname from other fields is that they are special fields and there's currently a limitation in re-filling special fields when using Advanced Error Handling.

By deriving from normal fields, this limitation is avoided.