Question: Jetcalculus package: Finding Lead derivatives.

I am working with the JetCalculus package along with the DifferentialGeometry package. Notation: if there are 2 independent variables (x,y), then u[1,2] would now represent the 3rd mixed partial derivative of u, once with respect to x and twice with respect to y. Please check Example 3 here, https://de.maplesoft.com/support/help/Maple/view.aspx?path=DifferentialGeometry/JetCalculus/TotalDiff

If I have an expression like u[1,0]+f(u[0,0])*u[0,1]+u[1,1]*u[0,3], then I am looking for a procedure which gives me the Lead derivative term. In the example above, it is u[1,1]*u[0,3], and then I can find the lead coefficient, i.e u[1,1].
Please note that the Lead derivative is not unique and can have several terms. For example, orders are the same for u[1,1] and u[0,2].

Idea: If I can find a way to extract the subscripts and do operations on them, then it would be very helpful. 
Any help/guidance is much appreciated. Thanks.
EDIT 1: LeadingDerivative command is not the solution for me.

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