     * @class doc_renamesidref_common
     *
     * Replaces all uses of a given @c SIdRef type attribute value with another
     * value.
     *
     * @copydetails doc_what_is_sidref
     *
     * This method works by looking at all attributes and (if appropriate)
     * mathematical formulas in MathML content, comparing the referenced
     * identifiers to the value of @p oldid.  If any matches are found, the
     * matching values are replaced with @p newid.  The method does @em not
     * descend into child elements.
     *
     * @param oldid the old identifier
     * @param newid the new identifier