"File Upload Limit" that can be set by WAF

Hello.

I'm collecting information about setting up WAF for Application Gateway v2.
I have three questions about the file upload limit in the WAF settings.

1.
What is the file upload limit? What does this file upload refer to?
For example, is it the maximum amount of files that can be uploaded from the file upload button defined by the HTML < input type = "file" > tag?

2.
What error will I get if I exceed this limit?

3.
What happens if I omit this setting (leave it blank)?
Will I be able to upload files without limit?

Thank you.