试试这种方法，也许会对你有帮助

$html_output = '<div class="element-item ' . $term . '">';
echo $html_output;

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试着这样

echo "<div class="element-item $term>";

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或
你可以在JavaScript的帮助下这样做

$(function(){
   $('.element-item').addClass('<?php echo $term ?>');
   });

型
如果你有什么问题，

您已经正确地识别了返回值方面的问题。
问题在这里：

$term = get_the_term_list( get_the_ID(), 'type' );

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get_the_term_list()将返回一个HTML字符串，如函数https://codex.wordpress.org/Function_Reference/get_the_term_list的文档中所述：
我建议采用以下方法：

// We're going to place all of our classes into this array.
$classes = array( 'element-item' );

// Get terms assigned to post.
$terms = get_the_terms( get_the_ID(), 'type' );

// Check terms were found.
if ( $terms && ! is_wp_error( $terms ) ) {

    // Loop through each found term and add it to the array of classes.
    foreach ( $terms as $term ) {
        $classes[] = $term->slug;
    }
}

// Convert the array of classes into a string separated by spaces.
// Escape the value before outputting inside the attribute tag.
printf( '<div class="%s">', esc_attr( implode( ' ', $classes ) ) );

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进一步阅读：https://codex.wordpress.org/Function_Reference/get_the_terms