message: docs(forms): clarify the description of `minLength` and `maxLength`
  Previously, it was not clear that the `minLength` and `maxLength` validators
  can only be used with objects that contain a `length` property. This commit
  clarifies this.
  PR Close
diff: @@ -267,7 +267,11 @@ export class Validators {
  * @description
  * Validator that requires the length of the control's value to be greater than or equal
  * to the provided minimum length. This validator is also provided by default if you use the
  - * the HTML5 `minlength` attribute.
  + * the HTML5 `minlength` attribute. Note that the `minLength` validator is intended to be used
  + * only for types that have a numeric `length` property, such as strings or arrays. The `minLength`
  + * validator logic is also not invoked for values when their `length` property is 0 (for example in
  + * case of an empty string or an empty array), to support optional controls. You can use
  + * the standard `required` validator if empty values should not be considered valid.
  *
  * @usageNotes
  *
  @@ -305,7 +309,8 @@ export class Validators {
  * @description
  * Validator that requires the length of the control's value to be less than or equal
  * to the provided maximum length. This validator is also provided by default if you use the
  - * the HTML5 `maxlength` attribute.
  + * the HTML5 `maxlength` attribute. Note that the `maxLength` validator is intended to be used
  + * only for types that have a numeric `length` property, such as strings or arrays.
  *
  * @usageNotes
  *
  