Access the query of a formDatasource in Dynamics Ax

We all know well that to access the datasource in a form we use table name suffixed by DS. But there is one another similar suffix that can help us access the datasource query. See example below to understand.

Eg:

//note the suffix "_q"used to access the query.
InventTable_q.datasourcetable(tablenum(InventTable)).addRange(fieldnum...

This is not widely used but can be of help at times.