StartsWith
Ensure the value of field under validation starts with a certain substr.
#Directive Code Snippet
<!DOCTYPE html>
<html lang="en">
...
<form (ngSubmit)="onSubmit(form)" #form="ngForm">
<input [startsWith]="<string to startWith>" type="text" name="<name>" [(ngModel)]="<name>" #<name>="ngModel">
</form>
...
</html>
#Chain Rule Code Snippet
<!DOCTYPE html>
<html lang="en">
...
<form (ngSubmit)="onSubmit(form)" #form="ngForm">
<input [Rule]="starts_with:<string to startWith>" type="text" name="<name>" [(ngModel)]="<name>" #<name>="ngModel">
</form>
...
</html>