Extend Script - How can I access the prefix of a prefix rule for a certain element

This is kind of a brute force method, but it looks like a prefix shows up in the list of the element's strings. If you know for sure that the element has a prefix, you can probably use something like this. Note that you may have to drop the delimiter between the prefix and the main element text from the end of the string.

#target framemaker

main ();

function main () {

    var doc, element, stringArray, prefix;
    
    doc = app.ActiveDoc;
    if (doc.ObjectValid () === 1) {
        element = doc.ElementSelection.beg.child;
        stringArray = (getAnArrayOfStrings (element, doc));
        prefix = stringArray[0];
        alert (prefix);
    }
}

function getAnArrayOfStrings (textObj, doc) {
    
    // Gets an array of strings from the text object or text range.

    var text, textItems, count, i;
    
    text = [];
    
    // Get a list of the strings in the text object or text range.
    if (textObj.constructor.name !== "TextRange") {
        textItems = textObj.GetText(Constants.FTI_String);
    } else {
         textItems = doc.GetTextForRange(textObj, Constants.FTI_String);
    }
    // Concatenate the strings.
    count = textItems.len;
    for (i = 0; i < count; i += 1) {
        text.push (textItems[i].sdata);
    }
    
    return text; // Return the array
}