Valid format for tel:? [SOLVED]

Ionic Framework ionic-v3
#1

It seems that tel:123-456-7896 is valid however tel:(123) 456-7896 is not
is there some doc that states the proper format for tel?

#2

RFC 3966?

#3

thanks, my problem was i wasnt putting {{}} in my href="tel:"
so it was not reading the right values