How do I know I've selected all text in the entire article?

Hi everyone.
When my cursor is in the current text box, it looks like this.
At this point, my current target of action, sel, is the current text box.

var doc = app.activeDocument;
var item = doc.selection[0];
var items;
alert(item.constructor.name);

if (
    ("InsertionPoint" == item.constructor.name
        || "Character" == item.constructor.name
        || "Text" == item.constructor.name
        || "Word" == item.constructor.name
        || "Paragraph" == item.constructor.name)
    && "Table" != item.parent.parent.constructor.name
) {
    items = item.parentTextFrames;
    sel = items;
    alert(items);

If I select all content in the current article,
Now, I want my selection target (sel) to be every text Frame of this article.

To be more precise, my target is the text box containing the selected text.
For example, if an article has 10 text boxes and I select content from boxes 3 through 6, then my target objects are Frame3, Frame4, Frame5, and Frame6.

How can I represent this with code?

Thank you.