<div *ngIf="isValid;else other_content">
content here ...
</div>
<ng-template #other_content>other content here...</ng-template>
<div *ngIf="isValid;then content else other_content">here is ignored</div>
<ng-template #content>content here...</ng-template>
<ng-template #other_content>other content here...</ng-template>
<div *ngIf="isValid;then content"></div>
<ng-template #content>content here...</ng-template>