Gform field value dynamically populate textarea for Body field

I am trying to dynamically populate the Body field for post data. I have followed the instructions here: http://www.gravityhelp.com/documentation/page/Gform_field_value_$parameter_name - but there is no documentation as to what field you should use for the gform_field_value. Below is the codes I have tried, but nothing works. i have checked off Allow field to be populated dynamically and the name of my parameter is "casedescription". Any ideas?

Is textarea correct?

add_filter("gform_field_value_textarea", "populate_casedescription");
function populate_casedescription($value){
return "This is incredible software if this works";
}

OR I tried this:
add_filter("gform_field_value_body", "populate_casedescription");
function populate_casedescription($value){
return "This is incredible software if this works";
}

Thanks very much. This worked great. I think you should update the instructions page for this to specifically state that the first argument in add_filter should be the parameter name of the field you want to pre-populate and the second the name of the function you are using. It's not clear form the examples on that page that this is what is needed (I was under the impression from that page that the first argument is the type of field).