Primeng区别：let-columns =“ columns” vs let-columns

Question

您能请我解释一下let-columns和let-columns =“ columns”之间的区别吗？在这两种情况下，模板都知道FOR的列

<p-table [columns]="cols" [value]="cars" (sortFunction)="customSort($event)" [customSort]="true">
    <ng-template pTemplate="header" let-columns>
        <tr>
            <th *ngFor="let col of columns" [pSortableColumn]="col.field">
                {{col.header}}
                <p-sortIcon [field]="col.field"></p-sortIcon>
            </th>
        </tr>
    </ng-template>
    <ng-template pTemplate="body" let-rowData let-columns="columns">
        <tr>
            <td *ngFor="let col of columns">
                {{rowData[col.field]}}
            </td>
        </tr>
    </ng-template>
</p-table>