Selecting default prompt text

[Richard Riley <rileyrgdev@gmail.com>]

I like my interactive functions to generally use the word or region at
point as a default. Is there a way to make the read-string mini buffer
input to pre-select the default value?

e.g

consider

(setq url (read-string (format "Url (%s) :" url) url nil url))

Here I would like to see at the input prompt

Url (xyz): xyz

with the default value of "xyz" already selected. In other words
the same behaviour as when you tab into a populated  entry field in most
of applications.