How is this bootbox even created?

I need to add some more inputs in a bootbox (which is in the picture bellow). However, I'm not able to find the html that "made it"

The message parameter it's filled with "<div class='dv_content'></div>" and nothing else

I don't know how this message can become this bootbox with so many inputs. For that I need you help understanding something that could be quite basic for some, but it isn't for me.

Let me give you more context

As you can see in the picture, there is a button. Once the button is clicked the bootbox is displayed. The function that it is called when the button is clicked is the following

As it is shown in the function body, it is creating a bootbox. Thus the question arises again. How can something as simple as "<div class='dv_content'></div>" can create that enormous bootbox?

By the code provided, it looks like it will be most likely be in form_agend(). The function can reference the variable as well as create event listeners for when the modal has opened and is visible or is in the process of opening.