Marker code to check, without its leading backslash (e.g. p, not \p)
true when the marker is a known USFM marker of type MarkerType.Paragraph.
false for anything else: character markers, note markers (f/fe/x), numbering markers
(v/va/vp/ca), and for empty or unknown marker codes.
True when a marker is a paragraph-style marker, including true discourse paragraphs, others that begin a block of text (poetry lines, blank lines, list entries, etc.) and chapter-level or book-level identification, metadata, or other such structural markers.
Paragraph markers are identified by their MarkerType.Paragraph type in usfmMarkers rather than a hand-maintained list.