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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def strip_el_text(el, max_depth=0, cur_depth=0):
 """Recursively strips the plain text out of the given XML etree element up to the desired depth. Args: el: The etree element to scan. max_depth: The depth to which to recursively strip text (default: 0). cur_depth: The current recursive depth to which we've scanned so far. Returns: The stripped, plain text from within the element. """

    # text in front of any child elements
    el_text = strip_str(el.text if el.text is not None else "")

    if cur_depth < max_depth:
        for child in el:
            el_text += " "+strip_el_text(child, max_depth=max_depth, cur_depth=cur_depth+1)
    else:
        # add the last child's tail text, if any
        children = list(el)
        if children is not None and len(children) > 0:
            if children[-1].tail is not None:
                el_text += " "+strip_str(children[-1].tail)

    # we skip the root element
    if cur_depth > 0:
        # in case there's any text at the end of the element
        if el.tail is not None:
            el_text += " "+strip_str(el.tail)

    return strip_str(el_text)