block_authorship        An authorship block (prepared-by line +
                        metadata)
block_flow_diagram      A model-development flow-diagram block
block_image             A block that embeds a raster image
block_keep              Keep a group of blocks together on one page
                        (atomic)
block_matrix            A wide-matrix block that groups columns to fit
                        the page width
block_para              A word-wrapped paragraph block
block_plot              A block that draws a base-R plot into a
                        reserved region
block_pre               A preformatted (monospace) block for
                        capture.output() dumps
block_rule              A horizontal rule spanning the frame width
block_signature         A signature / approval block (visible lines +
                        optional interactive fields)
block_spacer            A vertical spacer block
block_table             A table block with measured column widths and
                        automatic page splitting
flow_add                Add a single block imperatively
flow_run                Run a sequence of blocks through the flow
                        engine
frame_set               Set the content frame (and reset the cursor to
                        its top)
remaining               Vertical space remaining in the current frame
                        (points)
running                 Set the running header / footer
sp_add_sig_fields       Add interactive Acrobat signature fields to a
                        finished PDF
sp_close                Close the document (flush the PDF)
sp_figure_page          Draw a full-page multi-panel figure (outside
                        the flow engine)
sp_height               Line height (vertical advance) in points
sp_new                  Open a new simPDF document
sp_overlaps             Return overlapping text bounding-box pairs
                        recorded while tracing
sp_page                 Start a new page
sp_trace                Turn bounding-box tracing on for no-overlap
                        checks
sp_width                Measure text width in points
