FB 1.5

I have the following Domain:

CREATE DOMAIN DEFAULTUNIT AS
VARCHAR(3)
DEFAULT 'LB'
NOT NULL
CHECK (Upper(value) in ('LB','KG','OZ','GM','EA','M'))


From within my program I want to offer a combobox with these options
in a fixed dropdown list for fields that use this domain.

How can I extract the Check constraint from the System tables (or
maybe just the entire DML) so I can parse out the valid values?

Rick