Bolt 1: Clarify the definition of tu fields

Truncated integer fields, e.g. tu16 cannot have leading zeros
judging by the implementations of the parsers, which are used
across the different ln implementations.
The `can` imposed that it is not necessary to truncate the fields
to values of information.

Signed-off-by: Peter Neuroth <[email protected]>

Bolt 1: Add where tuXX fields may be used.

As truncated integers are not limited to TLV records with single
values (e.g. onion-routing payload type 8 - payment data) we want
to further clarify where the tuXX fields can be used.

Signed-off-by: Peter Neuroth <[email protected]>

Author: nepet

01-messaging.md

@@ -224,12 +224,12 @@ Various fundamental types are referred to in the message specifications:
 * `u32`: a 4 byte unsigned integer
 * `u64`: an 8 byte unsigned integer
 
-Inside TLV records which contain a single value, leading zeros in
-integers can be omitted:
+For the final value in TLV records, truncated integers may be used. Leading zeros in
+truncated integers MUST be omitted:
 
-* `tu16`: a 0 to 2 byte unsigned integer
-* `tu32`: a 0 to 4 byte unsigned integer
-* `tu64`: a 0 to 8 byte unsigned integer
+* `tu16`: a 0 to 2 byte truncated unsigned integer
+* `tu32`: a 0 to 4 byte truncated unsigned integer
+* `tu64`: a 0 to 8 byte truncated unsigned integer
 
 When used to encode amounts, the previous fields MUST comply with the upper
 bound of 21 million BTC: