Hi, this page is used to overwrite some fields and param in passed Report.

For example, u could change groupby fields without create new report ( so u can transform existing report in order what u need)  

With this parameter you can pass Virtual Report Page Name you created in your code.

for better clarification go through:

1. Open any thing from records 

2. Live UI on table 

3. check how report definition is invoked and clipboard