def cell(content, colspan=None, css_class=None, cell_id=None):
    """ Returns the given parameters as a well-formed HTML table cell tag.
        content: (str) The cell's inner content. Ex: Hello World!
        colspan: (int) HTML colspan tag content.
        css_class  : (str) HTML css class.
    """
    cell_str = '<td'

    if cell_id:
            cell_str += ' id="' + cell_id + '"'
    if colspan:
        cell_str += ' colspan=' + str(colspan)
    if css_class:
        cell_str += ' class="' + css_class + '"'

    cell_str += '>' + content + '</td>'
    
    return cell_str