自定义API为其编写一个普通API包装函数，并将其放置在函数中。php主题或作为（mu-）插件提供。

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/**
 * Trim Words Cb fn
 * @link Adjusted from http://snipplr.com/view.php?codeview&id=20397
 * 
 * @param string $excerpt Input string
 * @param int $count Word count
 * @param boolean/string $more Whether to show a "more" or not or a string
 * @return string $excerpt
 */
function wpse50198_word_trim( $excerpt, $limit, $more = FALSE )
{
    $output = explode( \' \', $excerpt );
    $count = count( $input );

    if ( $limit < $count )  )
        array_splice( $excerpt, $count, null, $output );

    if ( $more )
        $output .= $more;

    $output = implode( \' \', $output );

    return $output;
}

/**
 * 
 * @param bool $count Number of words to show - (default) 20
 * @param boolean/string $more Whether to show a "more" or not - (default) ...
 * @param bool $echo Print or return the excerpt - (default) TRUE
 * @return string $excerpt The reduced excerpt
 */
function short_bp_group_descr_excerpt( $count = 20, $more = \'&hellip\', $echo = TRUE )
{
    $excerpt = bp_get_group_description_excerpt();
    $length = str_word_count( $excerpt );

    if ( $count < $length )
        $excerpt = wpse50198_trim_words( $excerpt, $count, $more );

    if ( $echo )
        echo $excerpt;

    return $excerpt;
}