Trying to just get the matrix for operations in an fespace

General Discussion
1

from the documentation it looks like its possible to add customized finite element
types but just as a learning exercise, and I even had a specific usage in mind, is it
possible to dump the calculation of simple things like derivatives in an fespace?
For example, something like this,

`  1 : 
    2 : mesh Th = square(10,10);
    3 : fespace Xh(Th,P0);
    4 : matrix A=dx(Xh) error operator (  <PP5v_fes> 
 List of choices 
	 (	  <10LinearCombI6MDroit4C_F0E> :   <10LinearCombI6MDroit4C_F0E> )
	 (	  <St7complexIdE> :   <St4pairIP6FEbaseISt7complexIdE6v_fesLEiE> )
	 (	  <d> :   <St4pairIP6FEbaseId6v_fesLEiE> )
	 (	  <St7complexIdE> :   <St4pairIP6FEbaseISt7complexIdE6v_fesSEiE> )
	 (	  <d> :   <St4pairIP6FEbaseId6v_fesSEiE> )
	 (	  <St7complexIdE> :   <St4pairIP6FEbaseISt7complexIdE6v_fes3EiE> )
	 (	  <d> :   <St4pairIP6FEbaseId6v_fes3EiE> )
	 (	  <St7complexIdE> :   <St4pairIP6FEbaseISt7complexIdE5v_fesEiE> )
	 (	  <d> :   <St4pairIP6FEbaseId5v_fesEiE> )
	 (	  <10LinearCombI7MGauche4C_F0E> :   <10LinearCombI7MGauche4C_F0E> )