Slice 5 of #92. The last validator moves onto the framework and the legacy
Issue type is removed, so all validation now flows through one error model.
- ValidationError gains a severity (error by default, warning for advisory
findings), chosen so Schematron's assert/report distinction survives in the
unified type.
- Schematron is a Validation<Node, Void> over the document root; a failed assert
is an error finding, a matched report a warning. Each finding is located at the
context node its rule fired on (built from the element chain, with a sibling
index only when a name repeats), not the document root.
- Schematron.validate returns [ValidationError] and runs through a Validator.
- Validation.Issue and its Severity-based result are deleted; Severity now backs
ValidationError.
Every validation layer (structural, DTD, XSD content and identity, Schematron)
now produces located ValidationError values through the shared framework.
Add PureXML.Validation.Schematron: compile a Schematron schema (matching
schema/pattern/rule/assert/report by local name, so the ISO and legacy
namespaces both work) and validate a document. A rule's context XPath
selects the nodes it fires on; each assert/report test is evaluated relative
to the node via the XPath context-node API. A failed assert is an error, a
matched report a warning; within a pattern a node fires the first matching
rule. Adds XPath.Query.nodes(over:) returning matched tree nodes so one tree
can be queried repeatedly.
Closes#52Closes#53Closes#25
