def METHOD_NAME(self, category, stype="horizons"):
    """Clear (or make empty) the content of one or more horizon/zones... categories.
    Args:
        category (str or list): Name(s) of category to empty, either as
             a simple string or a list of strings.
        stype (str): 'Super type' in RMS (horizons or zones).
            Default is horizons
    .. versionadded:: 2.1
    """
    project = self.project
    categories = []
    if isinstance(category, str):
        categories.append(category)
    else:
        categories.extend(category)
    xtype = project.horizons
    if stype.lower() == "zones":
        xtype = project.zones
    for catg in categories:
        for xitem in xtype:
            try:
                item = xtype[xitem.name][catg]
                item.set_empty()
            except KeyError as kmsg:
                print(kmsg)