Key _Dynamic in
Tradable refers to a read only boolean flag that is normally FALSE
If TRUE, the tradable is not fully specified, with some of its specification parameters being context dependent.
For example, an object of type
Vanilla IRS has this flag set automatically to TRUE if its rate is left unspecified, in which case its effective rate becomes context dependent and set to a level implied by the prevailing market rates.
The TRUE setting ascribes a dynamic character to the contractual nature of the referenced tradable in the sense that the exact contract specifications are not fully defined by the tradable's contents but assume their values according to the context where the tradable is used.
In some sense, a dynamic tradable represents a well defined financial contract only within the context where it is used.
Prior to being used, it contains only the prescriptions that are capable of generating a well defined financial contract as soon as a context consisting of market data and modelling assumptions becomes available.

Note this key is prefixed by _, which indicates it is regarded as a read-only part of the object's data and therefore its associated value cannot be edited.
For that reason it does not appear as part of the input data.
It carries informational only value for the user and appears as part of its contents.
Also it completely depends on the remaining object contents and therefore is never part of the exported object's data.