Codes defining conditions on the _item_type.code specification.
'esd' permits a number string to contain an appended standard
deviation number enclosed within parentheses. E.g. 4.37(5)
'seq' permits data to be declared as a sequence of values
separated by a comma <,> or a colon <:>.
* The sequence v1,v2,v3,. signals that v1, v2, v3, etc.
are alternative values or the data item.
* The sequence v1:v2 signals that v1 and v2 are the boundary
values of a continuous range of values. This mechanism
was used to specify permitted ranges of an item in
previous DDL versions.
Combinations of alternate and range sequences are permitted.