Can't I pass the value via the field names including the `q?_` preceding it?

Can't I pass the value via the field names including the `q?_` preceding  it?

eg.   q?_myHiddenField 

Also... what are these for? 

They all seem funny when you have more than 1 hidden fields. 

UNIQUE NAME

{  }

FIELD IDs

#hidden_4

What is the form you are working on? The only way to pass the value from one field to another field in another form, is through the URL parameter as shown on this guide: https://www.jotform.com/help/351-How-to-Automatically-Pass-Form-Data-to-Another-Form