Parallel meanings within tags:
Within the 1XX, 4XX, 5XX, and 7XX blocks, certain parallels of content designation are usually preserved. The following meanings are given to the final two characters of the tag of fields in these blocks:
X00 Personal names
X51 Geographic names
X10 Corporate names
X55 Genre/form terms
X11 Meeting names
X80 General subdivisions
X30 Uniform titles
X81 Geographic subdivisions
X48 Chronological terms
X82 Chronological subdivisions
X50 Topical terms
X85 Form subdivisions