Implementation of Carsten Klee's MARCspec
MARCspec - A common MARC record path language
Carsten Klee (ZDB)
2017-11-20 (version 0.16beta+2)
https://marcspec.github.io/MARCspec/marc-spec.html
9.2 Reference to field data
fieldSpec = fieldTag [index] [characterSpec]
---
LDR field data of the leader
00.