Module validation 

DTD validation (§27, §85 Phase 6).

DTD validation against element/attribute declarations:

1. Element content model validation — does the element’s child sequence match its declared content model?
2. Attribute value validation — does each attribute’s value conform to its declared type (CDATA, ID, IDREF, IDREFS, ENTITY, ENTITIES, NMTOKEN, NMTOKENS, ENUMERATION, NOTATION)?
3. ID/IDREF consistency — are all ID values unique? Does each IDREF reference a valid ID?
4. Required attributes — are all REQUIRED attributes present?
5. NOTATION validation — are NOTATION attributes referencing declared notations?
6. Well-formedness constraints — additional validity constraints

UPSTREAM-PARITY

This module follows upstream libxml2 valid.c implementation. The validation context (xmlValidCtxt) accumulates ID/IDREF tables across the document and checks consistency in xmlValidateDocumentFinal.

Phase 6 status

Complete — all core DTD validation functions are implemented. Edge-case behavior for degenerate DTDs matches upstream.

Upstream contract

Mirrors upstream valid.c (SRC-LIBXML2-2.15.0-VALID-C, oracle tree oracle/historical/src/libxml2-2.15.0/valid.c): xmlValidateDocument, xmlValidateDtd, xmlValidCtxt ID/IDREF tables, xmlValidateElement, xmlValidateAttributeDecl and the content-model validation walks.

Conceptual behavior

DTD validation against element/attribute declarations: content-model matching, attribute value types (CDATA, ID, IDREF(S), ENTITY(IES), NMTOKEN(S), ENUMERATION, NOTATION), ID/IDREF consistency, REQUIRED attributes, NOTATION references and well-formedness constraints. The xmlValidCtxt accumulates ID/IDREF tables across the document and checks consistency in xmlValidateDocumentFinal.

Ownership & safety invariants

Ownership: the validation context owns its ID/IDREF table storage and error output; the document and declarations are borrowed. SAFETY: the recursive validation walks are depth-bounded (VALID_CTXT_DEPTH_MAX = 256) to avoid stack exhaustion on degenerate DTDs.

Historical quirks & epochs

E-005: –valid on an invalid document exits 3 from 2.13.0 (was 4); E-006: –valid with no DTD exits 0 from 2.15.0 (was 3) — the no-DTD-found failure stopped being exit-worthy. Parse-time ID/IDREF registration (xmlIsID/xmlAddID) was aligned with upstream in 11.1-N (R-000164); the _xmlElement mirror is 104 bytes (R-000139).

Deliberate oddities

Deliberate oddities: element-decl type_ carries XML_ELEMENT_DECL while etype holds the element type (upstream field split); ATTLISTs for undeclared elements create UNDEFINED placeholders not linked into the DTD children (xmlGetDtdElementDesc semantics).

Proving courts

DTD, RELAXNG and XSD court families; TREE-001 (ID/IDREF registration, atype = XML_ATTRIBUTE_ID), CLI-XMLLINT valid cases (exit codes 3/0 per E-005/E-006) and cargo test --lib.

Tempting simplifications that would break parity

A tempting simplification is skipping parse-time ID registration and resolving IDs lazily at validation time — it would break doc->ids fingerprints and xmlIsID semantics (R-000164). Do not unbounded the recursion: VALID_CTXT_DEPTH_MAX mirrors the hardened oracle (SD-002).

Structs

ContentModelExec

Runtime exec state for one open element’s content model.

ContentModelNfa

Incremental content-model matcher stored in _xmlElement.cont_model.

Functions

add_id^⚠

Upstream xmlAddID(ctxt, doc, value, attr) — returns the xmlID or NULL. Reports “ID %s already defined” through the validation context on duplicates and a memory error on OOM.

add_id_safe^⚠

Upstream xmlAddIDSafe(attr, value) (2.13+): add an ID without a validation context. Returns 1 on success, 0 if the ID already exists, -1 on OOM.

add_ref^⚠

Upstream xmlAddRef(ctxt, doc, value, attr) — registers an IDREF. Returns the xmlRef or NULL.

free_content_model_nfa^⚠

Free a compiled content-model NFA (called from xmlFreeElement).

free_id_table^⚠

Upstream xmlFreeIDTable(table).

free_ref_table^⚠

Upstream xmlFreeRefTable(table).

free_valid_ctxt^⚠

Free a validation context.

get_dtd_attr_desc^⚠

Upstream xmlGetDtdAttrDesc(dtd, elem, name) — attribute declaration lookup splitting the attribute QName into (local, prefix).

get_dtd_element_desc^⚠

Upstream xmlGetDtdElementDesc(dtd, name) — plain element declaration lookup with QName splitting.

get_dtd_notation_desc^⚠

Upstream xmlGetDtdNotationDesc(dtd, name).

get_dtd_qattr_desc^⚠

Upstream xmlGetDtdQAttrDesc(dtd, elem, name, prefix) — the attribute declaration table is keyed by (name, prefix, elem).

get_dtd_qelement_desc^⚠

Upstream xmlGetDtdQElementDesc(dtd, name, prefix).

get_id^⚠

Upstream xmlGetID(doc, ID): returns the attribute holding the ID, or the document pointer itself when operating on a stream (attribute node no longer exists).

get_refs^⚠

Upstream xmlGetRefs(doc, ID): returns the list of references for an ID.

is_empty_element^⚠

Check if an element is declared as EMPTY.

is_id^⚠

Upstream xmlIsID(doc, elem, attr): is this attribute an ID? Handles the HTML special cases (id attribute; name attribute on <a>) and the DTD declaration lookup, plus the xml:id namespace convention.

is_mixed_element^⚠

Check if an element has a mixed content model.

is_ref^⚠

Upstream xmlIsRef(doc, elem, attr): is this attribute an IDREF?

new_valid_ctxt^⚠

Create a new validation context.

remove_id^⚠

Upstream xmlRemoveID(doc, attr) — removes the attribute’s ID entry. Returns 0 on success, -1 otherwise.

remove_ref^⚠

Upstream xmlRemoveRef(doc, attr) — removes the attribute’s IDREF entry. Returns 0 on success, -1 otherwise.

set_valid_errors^⚠

Set error and warning callbacks on a validation context.

split_qname4^⚠

Split a QName at the FIRST ‘:’ (upstream tree.c xmlSplitQName4): prefix receives a duplicated prefix (or NULL) and the local name (a pointer into the original string) is returned.

validate_attribute_decl^⚠

Validate an attribute’s value against its declaration.

validate_attribute_value^⚠

Validate an attribute value against its declared type.

validate_build_content_model^⚠

Upstream xmlValidBuildContentModel(ctxt, elem): compile the element’s content tree into a content-model NFA cached in elem->contModel. Returns 1 on success, 0 on failure.

validate_content^⚠

Validate the content of an element node against its content model.

validate_document^⚠

Validate an entire document against its DTD.

validate_document_final^⚠

Final validation: check that all IDREFs resolve to existing IDs.

validate_dtd^⚠

Validate a DTD’s declarations (element/attribute declarations).

validate_dtd_final^⚠

Final DTD validation — checks ID/IDREF consistency.

validate_element^⚠

Validate a single element node against its DTD element and attribute declarations.

validate_element_decl^⚠

Upstream xmlValidateElementDecl(ctxt, doc, elem): verifies the declaration is not duplicated and that MIXED content models do not list the same element twice.

validate_enumeration^⚠

Validate that value is one of the values in the enumeration.

validate_id^⚠

Validate an ID value: check that the value is a valid XML Name and that no duplicate ID values exist in the document.

validate_id_ref^⚠

Validate an IDREF value: check that the referenced ID exists in the document.

validate_id_refs^⚠

Validate IDREFS (whitespace-separated list of IDREF values).

validate_name^⚠

Validate whether value is a valid XML Name.

validate_name_space^⚠

Modern 2-arg form, upstream tree.c xmlValidateName(value, space).

validate_name_value^⚠

Upstream xmlValidateNameValue(value) — 1 if valid, 0 otherwise.

validate_names^⚠

Validate whether value is a whitespace-separated list of XML Names.

validate_names_value^⚠

Upstream xmlValidateNamesValue(value) — 1 if valid, 0 otherwise.

validate_ncname^⚠

Modern 2-arg form, upstream tree.c xmlValidateNCName(value, space).

validate_nmtoken^⚠

Validate whether value is a valid XML NMTOKEN.

validate_nmtoken_space^⚠

Modern 2-arg form, upstream tree.c xmlValidateNMToken(value, space).

validate_nmtoken_value^⚠

Upstream xmlValidateNmtokenValue(value) — 1 if valid, 0 otherwise.

validate_nmtokens^⚠

Validate whether value is a whitespace-separated list of XML NMTOKENs.

validate_nmtokens_value^⚠

Upstream xmlValidateNmtokensValue(value) — 1 if valid, 0 otherwise.

validate_notation_decl^⚠

Upstream xmlValidateNotationDecl(ctxt, doc, nota): modern libxml2 has no validity constraint on notation declarations and returns 1 always (verified by disassembly of the system DSO: mov $1,%eax; ret).

validate_notation_use^⚠

Validate that notationName is a declared notation in the document’s DTD.

validate_one_attribute^⚠

Upstream xmlValidateOneAttribute(ctxt, doc, elem, attr, value).

validate_one_element^⚠

Upstream xmlValidateOneElement(ctxt, doc, elem) — validates a single element against its declaration (content model + attributes), WITHOUT recursing into children.

validate_one_namespace^⚠

Upstream xmlValidateOneNamespace(ctxt, doc, elem, prefix, ns, value) — namespace-declaration attribute validation.

validate_pop_element^⚠

Upstream xmlValidatePopElement(ctxt, doc, elem, qname): verify the parent content model completed and pop the validation state.

validate_push_cdata^⚠

Upstream xmlValidatePushCData(ctxt, data, len): character data is only legal as whitespace inside ELEMENT content.

validate_push_element^⚠

Upstream xmlValidatePushElement(ctxt, doc, elem, qname): validate a start tag against the parent’s content model and push the new element’s validation state.

validate_qname^⚠

Modern 2-arg form, upstream tree.c xmlValidateQName(value, space).

validate_root^⚠

Validate the root element of a document.