How does the el-table in element-ui realize the omission of excess content and add tooltip prompts?

Effect

description of renderings:
Only the title with more than 10 words will display the el-tooltip, and the ones without
exceeding 10 words will not be displayed Idea: The data in the table exceeds 10 words, display and hide, use the hover effect to display the el-tooltip and display all the text
Code:

     <el-table-column label="标题" width="180">
          <template slot-scope="scope">
            <el-tooltip
              class="item"
              effect="dark"
              :content="scope.row.title"
              placement="bottom"
              popper-class="tips"
            >
              <span v-if="scope.row.title.length >= 10">{
   
   {
                scope.row.title
              }}</span>
            </el-tooltip>
            <span v-if="scope.row.title.length < 10">{
   
   {
              scope.row.title
            }}</span>
          </template>
     </el-table-column>

/deep/.el-table td {
    border-bottom: 1px solid #2E2C3D;
    background: #242133;

    .cell span {
        display: block;
        width: 10em;
        overflow: hidden;
        white-space: nowrap;
        text-overflow: ellipsis;
    }
}

**Tips:** It can also be achieved by changing the em unit in the cell style to width, depending on the requirements.