Ok, now we throw in two real cool feature, regular expressions and numbered errortexts
The regex for the next field is: \d+{4}\s+[A-Z]{2}



HTML Code:

<HTML>
Ok, now we throw in two real cool feature, regular expressions and 
numbered errortexts<br> <FORM ACTION="http://www.flnet.nl/cgi-bin/tecform.pl" METHOD="POST">
<INPUT TYPE="hidden" NAME="mlto" VALUE="root">
<INPUT TYPE="hidden" NAME="mlheader_from" VALUE="mailform@invalid.domain">
<INPUT TYPE="hidden" NAME="mlheader_subject" VALUE="mailform test">
The regex for the next field is: \d+{4}\s+[A-Z]{2}<br>
<INPUT TYPE="text" NAME="field1:01:\d{4}\s+[A-Z]{2}"><br>
<INPUT TYPE="hidden" NAME="mlneeded:02" VALUE="field1">
<INPUT TYPE="text" NAME="field2"><br>
<INPUT TYPE="text" NAME="field3"><br>
<INPUT TYPE="hidden" NAME="mlneeded:02" VALUE="field2,field3">
<INPUT TYPE="hidden" NAME="mlerrtxt_01" VALUE="Hey, thats no good field 1 has an invalid value"> 
<INPUT TYPE="hidden" NAME="mlerrtxt_02" VALUE="Hey, you forgot some fields"> 
<INPUT TYPE="hidden" NAME="mltemplate" VALUE=
"This is a test template,
field1=@{field1}@, field2=@{field2}@, and field3=@{field3}@, 
You can put anny ascii char in this template :%44. 
There is a special way to send a @{%}@ .
.
You can also send an enviroment variable, you could be intrested
that the person who mailed this mail used: @{HTTP_USER_AGENT}@, and that 
his IP number is @{REMOTE_ADDR}@. 

bye. ">
<INPUT TYPE="submit">
</FORM>
</HTML>