The key “backscatter” will return an array with all the backscatter values in the BUFR tree, while:

/beamIdentifier=3/backscatter

will return the values of backscatter in the branch of the tree where the condition "beamIdentifier=3" is satisfied. 

If the condition is satisfied by more than one branch, all the values for all the branches satisfying the condition are returned.

As an example we can have in a TEMP message the need of getting the values of the temperature or humidity significant levels and this can be achieved by getting the values of the key:

/verticalSoundingSignificance=4/dewpointTemperature

This will return all the values of dewpointTemperature in the BUFR tree for which the verticalSoundingSignificance is 4.

Note: Only a single condition can be provided and it has to be of the form key=value (only the '=' operator is supported). The key has to be in the data section (not header key).