def combine_docs(docs):
    """
    Combine documents from a list of documents.
    Only combines if the element is a string.

    Parameters
    ----------
    `docs` : `list`. Documents to combine

    Returns
    -------
    `string` : Combined string of documents
    """
    combined_docs = ""
    for doc in docs:
        if isinstance(doc, str):
            combined_docs = combined_docs + doc
    return combined_docs