It checked that username match alpha regex or not
If you want to apply conditional validation on 'Contact Number' or 'Age', then you need to add 'userName' input as 'Bharat
{{userForm.controls?.userName?.errors?.onlyAlpha.message}}
It checked that age match with digit regex or not and it conditionaly applied when userName is Bharat
Conditional Expression with type 'string'
{{userForm.controls?.age?.errors?.onlyDigit.message}}