Trying to underline the rectangle of a Text Field

Question

I am trying to underline the rectangle of a Text Field with a Line Annotation, but I am a little confused.
The first doubt is about the "Square" vs, the "Rectangle" annotations. What is the difference between them? Has Adobe changed those recently?
I have tried several variations of the following snippet:
    var x1 = textField.rect[0];
    var y1 = textField.rect[1];
    var x2 = textField.rect[2];
    var y2 = textField.rect[3];
    var underscore = this.addAnnot({
        page: 0,
        type: "Line",
        rect: [x1, y1, x2, y1],
        strokeColor: color.red,
        strokeWidth: 160
What I am getting is an identity line (i.e., 45-degree) at the lower left corner.
-Ramon

Answer 1

Thanks for your reply, try67:
Could you -or anybody else- please clarify this:
"The square rect defines top-left-x, top-left-y, bottom-left-x and bottom-left-y.
For a line it's left-x, left-y, right-x, right-y."
According to such definition, the square rect does not contain any information about the right side?
Maybe what you meant to write is:
"The square rect defines:
top-left-x, top-left-y, bottom-right-x and bottom-right-y.
For a line it is
left-x, left-y, right-x, right-y."
If that's the case, a rect of zero height is the same thing as a horizontal line. That was my assumption, but I am getting a 45-degree line through the origin.
TIA,
-Ramon