A structure is defined by
DEFINE STRUCTURE A
and any element then by
DEFINE REAL A%B
Sub-structures can be defined, too
DEFINE STRUCTURE A%C
DEFINE REAL A%C%E
An entire structure (e.g. A as above) and all its element can be deleted using
DELETE /VAR A
Structures can be assigned as a whole by command LET. This command will copy all elements of the same name, and leave the others untouched. HEADERs are actually special structures.