CLDR-18008 Specify that currency digits might not be derived from ISO…

… 4217 (#4112)

docs/ldml/tr35-numbers.md

@@ -946,7 +946,10 @@ Each `currencyData` element contains one `fractions` element followed by one or
 The `fractions` element contains any number of `info` elements, with the following attributes:
 
 * **iso4217:** the ISO 4217 code for the currency in question. If a particular currency does not occur in the fractions list, then it is given the defaults listed for the next two attributes.
-* **digits:** the minimum and maximum number of decimal digits normally formatted. The default is 2. For example, in the en_US locale with the default value of 2 digits, the value 1 USD would format as "$1.00", and the value 1.123 USD would format as → "$1.12".
+* **digits:** the minimum and maximum number of decimal digits normally formatted. 
+The default is 2. 
+For example, in the en_US locale with the default value of 2 digits, the value 1 USD would format as "$1.00", and the value 1.123 USD would format as → "$1.12". 
+This value of this field is based on the "minor unit" value from ISO 4217, but may deviate from ISO 4217 where there is compelling evidence for different customary practice.
 * **rounding:** the rounding increment, in units of 10<sup>-digits</sup>. The default is 0, which means no rounding is to be done. Therefore, rounding=0 and rounding=1 have identical behavior. Thus with fraction digits of 2 and rounding increment of 5, numeric values are rounded to the nearest 0.05 units in formatting. With fraction digits of 0 and rounding increment of 50, numeric values are rounded to the nearest 50.
 * **cashDigits:** the number of decimal digits to be used when formatting quantities used in cash transactions (as opposed to a quantity that would appear in a more formal setting, such as on a bank statement). If absent, the value of "digits" should be used as a default.
 * **cashRounding:** the cash rounding increment, in units of 10-cashDigits. The default is 0, which means no rounding is to be done; and as with rounding, this has the same effect as cashRounding="1". This is the rounding increment to be used when formatting quantities used in cash transactions (as opposed to a quantity that would appear in a more formal setting, such as on a bank statement). If absent, the value of "rounding" should be used as a default.