These are for use in the TEXT segments. None are required, but if any of these identifiers are present they must confirm to the description below. Much (currently all) of this list has been taken from the NCBI Trace Archive  documentation. It is duplicated here as the ZTR spec is not tied to the same revision schedules as the NCBI trace archive (although it is intended that any suitable updates to the trace archive should be mirrored in this ZTR spec).
The Trace Archive specifies a maximum length of values. The ZTR spec does not have length limitations, but for compatibility these sizes should still be observed.
The Trace Archive also states some identifiers are mandatory; these are marked by asterisks below. These identifiers are not mandatory in the ZTR spec (but clearly they need to exist if the data is to be submitted to the NCBI).
Finally, some fields are not appropriate for use in the ZTR spec, such as BASE_FILE (the name of a file containing the base calls). Such fields are included only for compatibility with the Trace Arhive. It is not expected that use of ZTR would allow for the base calls to be read from an external file instead of the ZTR BASE chunk.
[ Quoted from TraceArchiveRFC v1.17 ]
Identifier Size Meaning Example value(s) ---------- ----- ---------------------------- ----------------- TRACE_NAME * 250 name of the trace HBBBA1U2211 as used at the center unique within the center but not among centers. SUBMISSION_TYPE * - type of submission CENTER_NAME * 100 name of center BCM CENTER_PROJECT 200 internal project name HBBB used within the center TRACE_FILE * 200 file name of the trace ./traces/TRACE001.scf relative to the top of the volume. TRACE_FORMAT * 20 format of the tracefile SOURCE_TYPE * - source of the read INFO_FILE 200 file name of the info file INFO_FILE_FORMAT 20 BASE_FILE 200 file name of the base calls QUAL_FILE 200 file name of the base calls TRACE_DIRECTION - direction of the read TRACE_END - end of the template PRIMER 200 primer sequence PRIMER_CODE which primer was used STRATEGY - sequencing strategy TRACE_TYPE_CODE - purpose of trace PROGRAM_ID 100 creator of trace file phred-0.990722.h program-version TEMPLATE_ID 20 used for read pairing HBBBA2211 CHEMISTRY_CODE - code of the chemistry (see below) ITERATION - attempt/redo 1 (int 1 to 255) CLIP_QUALITY_LEFT left clip of the read in bp due to quality CLIP_QUALITY_RIGHT right " " " " " CLIP_VECTOR_LEFT left clip of the read in bp due to vector CLIP_VECTOR_RIGHT right " " " " " SVECTOR_CODE 40 sequencing vector used (in table) SVECTOR_ACCESSION 40 sequencing vector used (in table) CVECTOR_CODE 40 clone vector used (in table) CVECTOR_ACCESSION 40 clone vector used (in table) INSERT_SIZE - expected size of insert 2000,10000 in base pairs (bp) (int 1 to 2^32) PLATE_ID 32 plate id at the center WELL_ID well 1-384 SPECIES_CODE * - code for species SUBSPECIES_ID 40 name of the subspecies Is this the same as strain CHROMOSOME 8 name of the chromosome ChrX, Chr01, Chr09 LIBRARY_ID 30 the source library of the clone CLONE_ID 30 clone id RPCI11-1234 ACCESSION 30 NCBI accession number AC00001 PICK_GROUP_ID 30 an id to group traces picked at the same time. PREP_GROUP_ID 30 an id to group traces prepared at the same time RUN_MACHINE_ID 30 id of sequencing machine RUN_MACHINE_TYPE 30 type/model of machine RUN_LANE 30 lane or capillary of the trace RUN_DATE - date of run RUN_GROUP_ID 30 an identifier to group traces run on the same machine [ End of quote from TraceArchiveRFC ] More detailed information on the format of these values should be obtained from the Trace Archive RFC .