Need Help in using Aguascalientes Online Archive in more detail can someone please help?

Someone has posted an Aguascalientes online archive which is this:

http://sigue.aguascalientes.gob.mx/axweb/

to get in username: sigue.publica
password: publica

I have been using it to look through:

"lugar"
"tipo documental"
"fondo"

What I would like to know is how to use the other search fields such as:

"Escritura"