IMAP URL for text fragment

``` The URL: <imap://minbari.example.org/gray-council;UIDVALIDITY=385759045/; UID=20/;PARTIAL=0.1024>

may result in the following client commands and server responses:

<connect to minbari.example.org, port 143> S: * OK [CAPABILITY IMAP4rev1 STARTTLS AUTH=ANONYMOUS] Welcome C: A001 AUTHENTICATE ANONYMOUS S: + C: c2hlcmlkYW5AYmFieWxvbjUuZXhhbXBsZS5vcmc= S: A001 OK Welcome sheridan@babylon5.example.org C: A002 SELECT gray-council <client verifies the UIDVALIDITY matches> C: A003 UID FETCH 20 BODY.PEEK[]<0.1024> ```

ABNF: abnf partial-range = number ["." nz-number] ; partial FETCH. The first number is ; the offset of the first byte, ; the second number is the length of ; the fragment.