How does ElementUi use slot= "header"?

1Jing ElementUI wants to customize the header, which is officially done like this

  <el-table :data="tableData" stripe border highlight-current-row  class="drag_table" style="width: 100%;margin-top:20px;">
          <el-table-column v-for="(item, index) of tableHeader" :prop="item" :label="item" :key="index"
                           :column-key="index.toString()"  >
            <template slot="header" slot-scope="slot">
                {{ slot }}
            </template>


          </el-table-column>

        </el-table>

what I want to ask is, how do I get the injected value, for example, how to implement the original header lable, that I want to define is xx+?

Oct.17,2021

if you customize the header, you can refer to this form

  < / template >  cannot be displayed in this way, and examples on element-ui cannot be copied directly. Is there anything else you need? Or does it have something to do with the version of element-ui? 

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