select_block_conversion_impl
============================

Convert from a blocked\_representation to its inner\_representation by 
selecting 
a 
block based on its position, taking a slice of the input pattern.  In counting the
position, zero/empty blocks are ignored, and counting can be from the left or right
end.

get_position
============

	some_sbc get_position

Print the currently set position for the block to be extracted.

set_position
============

	some_sbc set_position block_number

Indicate the direction and distance of travel in finding a zero block when
applying `some_sbc`.  For `block_number`, 0 is the first non-zero block from
the left, 1 the second, and so on.  -1 is the first non-zero block from the
right, -2 the second, and so on.