Official DIGGS instance fixtures synced from https://github.com/DIGGSml/diggs-examples
by scripts/sync_reference.py. The pinned upstream commit, the upstream path of every
file and its sha256 are in PROVENANCE.toml; `python scripts/sync_reference.py check`
verifies them.

Layout:
  2.5.a/  — schema-valid Diggs instances against Complete.xsd
  2.6/    — schema-valid Diggs instances against Diggs.xsd (2.6 NS)
  3.0/    — schema-valid Diggs instances against Diggs.xsd (schemas/3 NS → 3.0.0)
  known_invalid/ — official examples that are not acceptable Diggs documents
                   (schema fail, or a non-Diggs GML root accepted only via
                   Diggs.xsd GML imports — rejected via context_check)

Local corrections (applied by the sync script; drop when diggs-examples merges them):
  2.6/PorePressureDissipationOnly.xml
  2.6/PorePressureDissipation.xml
  2.6/CPT_and_PorePressureDissipation.xml
    — t50 uom kPa → s (matches 3.0 example; DIGGSml/diggs-examples#4)
    — coef_consolidation_horiz keeps schema AllUnits spelling cm2/m (2.6 Kernel.xsd
      documents this as cm²/minute); dictionary check 12 aliases cm2/m → cm2/min

Known upstream defects (pinned in tests, not corrected):
  known_invalid/3.0_PileDrivingExample_schema-dev.xml
    — rewritten upstream (2026-08-23) with DIGGSml/schema-dev types (elevations as
      PointLocation) while still declaring the released 3.0.0 schema, so it fails
      3.0.0 schema validation.
  3.0/PorePressureDissipation_Example.xml
    — uses eight codes the official dictionaries do not define (dictionary check 5).
      pyDIGGS 1.1.1 and earlier hid this with local additions to properties.xml and
      roles.xml; those were removed when the dictionaries were re-synced.
