Expand description
Namespace handling (§23, §85 Phase 2/3).
Default namespace, prefixed namespace, namespace undeclaration, attribute namespaces, duplicate declarations, shadowing, prefix reuse, conflicting prefixes, orphaned namespace pointers, namespace reconciliation.
Phase 0: scaffolded. Implementation begins in Phase 2/3.
§Upstream contract
Mirrors upstream namespaces.c (SRC-LIBXML2-2.15.0-NAMESPACES-C, oracle
tree oracle/historical/src/libxml2-2.15.0/namespaces.c): xmlNewNs,
xmlSetNs, xmlSearchNs, xmlSearchNsByHref, xmlGetNsList,
xmlReconciliateNs, xmlCopyNamespace, xmlCopyNamespaceList,
xmlFreeNamespace, xmlFreeNamespaceList, xmlNewGlobalNs.
§Conceptual behavior
Default namespace, prefixed namespace, namespace undeclaration, attribute namespaces, duplicate declarations, shadowing, prefix reuse, conflicting prefixes, orphaned namespace pointers and namespace reconciliation. Namespace nodes live on node->nsDef chains and are resolved by walking the element scope upward — the same model the parser and XPath rely on.
§Ownership & safety invariants
Ownership: an xmlNs created by xmlNewNs is owned by the node nsDef list and freed with the node (xmlFreeNs only for unlinked standalone ns); node->ns is a borrowed pointer. SAFETY: upstream xmlNs nodes have NO parent pointer (QUIRK-0002 / LORE-0006) — the model must not invent one.
§Historical quirks & epochs
The no-parent namespace node is a long-standing upstream divergence fixed only in the c14n birth commit 044fc6b7 (2002, issue #61290); downstream XPath namespace-axis consumers depend on it. Epoch: unchanged across 2.7.8 to 2.15.3 (stable case in the historical matrix).
§Deliberate oddities
The deliberately odd part is the nsDef-first resolution order used by xmlSAX2AttributeNs (R-000147): scan the element-local declarations, then fall back to the parent scope — the new element is not yet linked to its parent when attributes are processed.
§Proving courts
Exercised by the TREE-NS-* and XPATH-NS-* court families (QUIRK-0002),
TREE-001 (nsDef duplicates, empty-value xmlns, default-ns handling),
READER-001 (attribute namespace accessors) and cargo test --lib.
§Tempting simplifications that would break parity
A tempting simplification is giving namespace nodes a parent pointer for convenience — it would break XPath 1.0 namespace-axis semantics and the TREE-NS-* courts. Do not deduplicate nsDef entries: upstream registers each declaration once and TREE-001 fingerprints the exact chains.