Structure of tel: URI

Hello All

Why does the tel: URI has no definition of the whole number (something like address-signal), but the separated phonedigits? So it could be something like this:

subscriber          =  global-number / local-number
global-number       =  global-number-part [isdn-subaddress]
global-number-part  =  "+" address-signal
local-number        =  local-number-part [isdn-subaddress]
                       [context]
local-number-part   =  address-signal
address-signal	  =  1*phonedigit

Greetings,
Denis Alexeitsev