Fields within structures may be added, deleted or modified, using operators (+, -, *, -+, *+). This allows Trace Headers to be extensible.

 Operator   Definition
 --------   ----------
 +          append members named by the operand
 -          delete all previous members named by the operand
 *          replace members named by the operand
 -+         delete and append members named by the operand
 *+         replace  or append members named by the operand
    

Operators are processed from left to right. For example given:

typedef struct {int   a, b, c;} old_xyz;
typedef struct {float d, e, f;} add_xyz;
typedef struct {void  b, e;} drop_xyz;
    

typedef struct { + old_xyz; + add_xyz; - drop_xyz;} drop_xyz;
    

typedef struct {int   a, c; float d, f;} xyz;
    

The end user may explicitly add, drop or modify fields in the generic DDS format simply by specifying the Definition, "MOD_FIELD". For example, the following Definition will add (or modify) headers "a" and "b" in the structure as floating point values, add (or replace at the end) header "c" as an integer value and drop head "d" all together.

MOD_FIELD= *+ float a, b; -+ int c; - void d;