Gets a list of valid plot layouts for the current work session.
(map_pltblklist)
Returns the names of the blocks in a list or nil.
This function returns the plot layout (block) names that are usable as plot layouts. To qualify, a block must have at least one unique viewport on one of its layers. That is, if the block has more than one viewport, it must have one layer that contains only one viewport.
The unique viewport can share its layer with objects of other types, such as lines, polylines, blocks, and text.