Custom Dialog Dynamic Stamp - Dropdown Menu

Hi there.

1) I have a dynamic stamp with JS script implemented in it, and I wanted to add a field with a drop-down Menu in it. Any help please? I don't even know what to put for type etc (like the code below(#2)).

2) Also I have another question: is there a way to limit the length of characters to a number lets say 200, and the rows to a number lets say 5?

 {
 type: "edit_text",
 item_id: "whatever",
 variable_Name: "m",
 multiline: "true",
 width: 400,
 height: 23,
 char_width: 8
 },

If you could do a single menu example with (A,B,C choices) I would really appreciate it.
I've already read about the Popup dialog in the documentation, but I don't know how to implement a drop-down version it in the dynamic stamp.