Substruct Selectors

A substruct selector is an expression that implicitly or explicitly removes certain parts from the JSON structures that define the output of a given time series type.

The following substruct selectors are available:

hdrshow	implicitly drops parts from the header (by keeping the specified ones)
hdrhide	explicitly drops parts from the header
obsshow	implicitly drops parts from the observation (by keeping the specified ones)
obshide	explicitly drops parts from the observation

MORE DETAILS AND EXAMPLES TO BE ADDED HERE!