angular - Angular2 Directive - selector with multiple ids -

i'm implementing custom directive in angular 2, directive form validation, , in many places see in directive definition selector property associated multiple ids - example:

@directive({     selector: '[my-custom-validator][ngmodel]' }) 

what multiple '[...]' (brackets) selection mean?

as in css, selector [attr] matches elements have attribute named attr. when multiple attribute selectors chained together, all attributes must exist on element.

note: unlike css, angular ignores [...] or [(...)] binding brackets on target attribute when performs match.

thus, selector [my-custom-validate][ngmodel] matches elements have both my‑custom‑validate attribute , ngmodel attribute (including [ngmodel] , [(ngmodel)]). example, selector matches

 <input type="text" name="username" my-custom-validate [(ngmodel)]="model.username"> 

but not

 <input type="text" name="username" my-custom-validate>