520 SUMMARY, ETC. (R)Indicators First Display constant controller ^ No information provided 0 Subject 1 Review 2 Scope and content 3 Abstract 8 No display constant generated Second Undefined; contains a blank (^)Subfield Codes $a Summary, etc. note (NR) $b Expansion of summary note (NR) $u Uniform Resource Identifier (R) $z Source of note information (NR) [OBSOLETE] $3 Materials specified (NR) $6 Linkage (NR) $8 Field link and sequence number (R)